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Full text of "Plant life, considered with special reference to form and function"

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LARCH AND BUR OAK, SHOWING TWO TYPES OP' 
MONOPODIAL BRANCHING. 



(■Sr*/.8 7 .) 



PLANT LIFE 

CONSIDERED WITH SPECIAL REFERENCE TO 
FORM AND FUNCTION 



BY 

CHARLES REID BARNES 

Professor of Plant Physiology in the University of Chicago 



NEW YORK 

HENRY HOLT & COMPANY 
1898 



Copyright, 1898, 

BY 

HENRY HOLT & CO. 



ROUBHT DKUHHiiNI) I'KINTHR, NKV 



PREFACE. 

In recognition of the fact that the study of botany in the 
past has been too much a study of books about plants, numer- 
ous laboratory manuals have been published which make pos- 
sible the study of plants themselves. Laboratory work has 
now become well-nigh universal. With the strenuous insist- 
ence that this method should be used in the secondary schools, 
there has been a growing danger that such study would de- 
generate into mere memory training, unless the relation of 
the facts, often entirely isolated in the pupil's mind, were 
clearly brought out. Since laboratory study soon came to 
include the examination of the lower plants as well as seed 
plants, and has now begun to include some experiments in 
their physiology, the absence of an elementary account of 
the form and functions of plants of all groups has made itself 
felt. I am not aware that any book at present attempts to 
meet this need. 

To the proper teaching of botany in secondary schools 
such a book is indispensable. However capable the teacher 
may be to gather up the facts observed in the laboratory and 
to relate them with others so as to produce a clear concep- 
tion of plant life, he cannot wisely rely upon the lecture for 
pupils of 13 to 18 years. They need the printed page, 
which appeals to eye as well as ear, if the principles and facts 
are to be firmly grasped. 

iii 



IV PREFA CE. 

Plant Life is an attempt to exhibit the variety and pro- 
gressive complexity of the vegetative body; to discuss the 
more important functions; to explain the unity of plan in 
both the structure and action of the reproductive organs ; 
and finally to give an outline of the more striking ways in 
which plants adapt themselves to the world about them. I 
have made an effort to treat these subjects so that, however 
much the student may have still to learn, he will have little 
to unlearn ; for eradication of false notions is the despair of 
the college teacher of science. 

This is not a book to be memorized and recited. If so used it 
is abused. It aims to be intelligible to pupils 13 to 18 years 
of age who are engaged in genuine laboratory study — not at 
irregular hours, without supervision, in a school desk, or at 
home, but in a suitable laboratory, with regular time (an 
hour and a half daily if possible), under the direction of a 
live teacher who has studied far more botany than he is 
trying to teach. I am aware that such conditions are yet 
unrealized in many schools ; but they may be gradually 
reached. That Plant Life may prove useful in botanical 
instruction even under the most unfavorable conditions, I 
permit myself to hope rather than to expect. 

This book may be used to supplement any laboratory guide 
or the directions prepared by the teacher. For the sake of 
teachers who may not wish to use two books, or who lack time 
and facilities for preparing laboratory directions, I have out- 
lined a course of study in Appendix I which can be carried 
out with the equipment listed in Appendix III. A description 
of the material needed and of suitable methods of preserving 
it forms Appendix II. Each'teacher will, of course, need to 
modify the directions to suit the material available. I have 
always found it easier to prepare directions to fit the material 
than to create the material to fit the directions. The "dem- 
onstrations " of Appendix I air intended as suggestions to the 



rREFA CE. V 

teacher of things which it is advisable to show to pupils under 
the compound microscope, in case inadequate equipment, 
lack of time, or difficulty of preparation forbid class study. 

I have made the directions fullest in relation to cryptogams 
and physiology because these fields are most unfamiliar to 
teachers at present. Further directions for the study of seed 
plants can readily be provided from the books listed in Ap- 
pendix IV. 

For laboratory study it is necessary to select certain illus- 
trative types and observe their structure. In the text I have 
not specifically discussed these plants, but have treated gen- 
eral topics so as to correlate the facts gained by a study of 
types with others which can be readily interpreted by means 
of the experience in the laboratory. References from the 
bare directions of Appendix I to the paragraphs and figures 
of the text are abundant and are intended to aid the student 
in the comprehension of the type under observation. It may 
be objected that he is thus aided too much. But I believe 
that in his first steps in laboratory training the student re- 
quires a large amount of help, and that its results are more 
often nullified by too little assistance than by too much. 

In the text I have neither sought nor avoided the use of 
technical terms. I have refrained from making the book a 
mere illustrated glossary. Yet I see no advantage, even for 
young students, in repeated circumlocution, for which a 
single word might stand. Definitions of most of the tech- 
nical terms used may be found by means of the index ; 
others are defined in the standard dictionaries. The careful 
teacher will insist upon a clear understanding of the meaning 
of terms and the accurate use of language. 

I have refrained from frequent citation of plants by name 
as examples of facts stated, chiefly because beginners are 
rarely familiar with any plants except the commonest domes- 
ticated ones and a few forest or shade trees. 



VI PREFACE. 

No apology is necessary for the exclusive use of the metric 
system. If pupils lack familiarity with it, the actual handling 
of metric measures and weights will soon remedy this. A 
useful chart showing the units may be obtained of the Ameri- 
can Metrological Society, 41 East Forty-ninth Street, New 
York, for ten cents. 

Very few of the illustrations are original. In the main they 
have been selected from a wide range of standard works with 
especial care to secure accuracy and clearness. Whenever 
possible the source of the figure and its magnification have 
been given. The attention of the teacher is invited to the 
very full description which accompanies each figure. In 
these explanations will be found much matter which is often 
put into subordinate paragraphs in other books. I have ob- 
served that students are prone merely to " look at " figures, 
and rarely study them. I therefore suggest that real study of 
the illustrations as supplementing the text be insisted upon. 
Sections are apt to be puzzling to beginners unless they are 
taught how to interpret them. This can be done by requir- 
ing them to sketch on paper or blackboard imaginary sections 
of common objects in different planes. Articles of regular 
form, such as a pencil, book, slate, ink bottle, desk, etc., 
may be ''sectioned," until from sketches of sections in three 
planes at right angles the student can construct a mental 
image of the object. 

Although divided into four parts, it has not been possible 
to keep the subject matter of each wholly distinct, since 
morphology, physiology and ecology are so interrelated. In- 
deed it has been thought best to combine the morphology 
and physiology of the reproductive organs to form Part III, 
rather than to divide it between two. The teacher will do 
well to see that the pupil does not neglect the abundant cross 
references. 

While the whole book is simply a restatement of widely 



PREFACE. VI 1 

known facts, for which I am mainly indebted to general 
treatises, monographs and shorter papers, I am constrained 
to acknowledge for Part IV my special indebtedness to 
Warming's Lehrbuch der bkologischen Pflanzengeographie and 
Ludwig's Lehrbuch der Pjlanzenbiologie. 

C. R. B. 
University of Chicago. 



CONTENTS. 



Preface 



PAGE 

, iii 



PART I: THE PLANT BODY. 



Introduction : The unit of structure 
Chapter I. Single-celled plants and colonies 
II. Linear and superficial aggregates 

III. The thallus of the higher alg^e . 

IV. The fungus body of hyphal elements 
V. Liverworts and mosses 

VI. Fernworts and seed plants 
VII. The root .... 
VIII. The shoot .... 
IX. The stem .... 



X. The leaves 



17 
26 
39 
49 
60 
65 
82 
96 
"7 



PART II : PHYSIOLOGY. 



Chapter XL Introduction : The unit of function 
XII. The maintenance of bodily form 

XIII. Nutrition 

XIV. Growth 

XV. The movements of plants 



M3 

147 
151 
178 

18S 



PART III: REPRODUCTION. 



Chapter XVI. Introduction : Reproductive structures . 209 
XVII. Vegetative reproduction . . . .211 

XVIII. Sexual reproduction 268 

ix 



CONTENTS. 



PART IV : ECOLOGY. 

PAGE 

Chapter XIX. Forms of vegetation 30S 

XX. Mesophytes 312 

XXI. Xerophvtes and halophytes . . . 318 
XXII. Hydrophytes 327 

XXIII. Adaptations to other plants as supports 330 

XXIV. Symbiosis 333 

XXV. Animals as food, foes, or friends . . 342 

XXVI. Protection and distribution of spores 

and seeds 352 

Appendix I. Directions for laboratory study . . . 369 
II. Directions for collecting and preserving 

material 401 

III. Apparatus and reagents 409 

IV. Reference books 413 

V. Outline of classification .... 415 

Index 4*9 



PLANT LIFE. 



PART I: THE PLANT BODY. 

INTRODUCTION. 

1. Units of structure. — An examination of any plant by 
proper methods reveals the fact that it is made up of one or 
more units of structure. The unit of structure of a brick 
wall is the individual brick. Each has a definite shape and 
relation to others, upon which the form of the wall depends. 
The unit of structure of a plant is called a cell. The cells 
have each a definite form and relation to others, and upon 
these two factors the form of the entire plant depends. 

But between the plant and the brick wall there is this im- 
portant difference. The bricks, after being perfectly formed, 
were put together. The cells of the plant are produced where 
they lie and gradually groiv to a mature form and size. The 
bricks are originally disconnected ; the plant-cells are con- 
nected by origin, and only as they become mature do they 
separate, if at all. 

2. The cell. — A plant-cell is a minute portion of living 
matter, called protoplasm or plasma, generally surrounded by 
a membrane, called the cell-wall (fig. i). If the brick in 
the previous illustration be taken to represent the protoplasm, 
the mortar may be considered as the cell-wall. * 

* This illustration must lie carried no further than to show the relation 
of position of these two parts of a cell. 




2 PLANT LIFE. 

3. Protoplasm. — The protoplasm is the essential part of 
the cell. It constructs the cell-wall. Rarely, if ever, is it 
uniform throughout, but is differentiated into distinct mem- 
bers, each having special work to do. In the most com- 
pletely differentiated active cells the 
greater part of the protoplasm con- 
sists of a finely granular or nearly 
transparent, colorless portion, called 
cytoplasm. Embedded in the cyto- 
plasm are the nucleus, centrospheres 
(figs, i and 2), and plastids (figs. 
3 to 8). 

Fig. i.-a ceil (the megaspore) 4. Cytoplasm. — This is not a 
^anuiar'protopiasm^'^vvhich single substance, but a mixture of 
L^tnuintnrfnuci:' several different substances, so in- 
ce^,^T n, The y iVn: timately mixed and so unstable that 
^s n fhe th c e e.rwln pl ^th r t e h P os e e' it is not possible to analyze it. 
el the M a a d inffie n d "oo diam!- Moreover, the nature and amount 

After Gufgnard. Qf t j ]e components are probably 

variable. Most of the substances belong to the class of com- 
pounds called proteids, so that cytoplasm responds to proteid 
tests and is often spoken of as a mixture of proteids. In 
addition there are frequently present other organic substances 
(such as amides, carbohydrates, fats, and enzymes), and 
always small quantities of mineral matters which appear as 
ash when cytoplasm is completely burned. The minute 
granules embedded in the cytoplasm are of various nature. 
Most of them are solid substances. 

5. Vacuoles. — Scarcely distinguishable from these at first 
are the minute cavities, called vacuoles, filled with dilute 
watery solutions of many different substances, the cell- sap. 
In all but the youngest cells more or fewer of these bubbles 
of water may unite to form larger ones (fig. 7). These often 
increase so as to occupy the greater part of the space within 



INTKODLCI/O.V. 3 

the cell-wall, being separated only by plates of protoplasm. 
When all vacuoles fuse into one the cytoplasm is crowded as 
a thin layer against the wall, with sometimes strands of it 
crossing the vacuole as the remnants of the plates at an 
earlier stage (fig. 188). 

6. Nucleus. — The nucleus varies much in shape. In cells 
whose diameters are nearly equal, it is generally spherical 
or ovoid, but in elongated cells it may become spindle- 
shaped or cvlindric. It is surrounded by a very delicate 
membrane, and is composed of two sorts of substances, one 
of which can be readily stained by certain liquid dyes, while 
the other usually remains uncolored (fig. 2). The nucleus 




Fig. 2. — A part of the same cell as in fig. i, but older, with the nucleus beginning to 
divide. The dark thread in A, separated into pieces in />. represents the chroma 
tin of the nucleus deeply stained, the rest of the nuclear material being unstained. 

a, centrospheres. Magnified f diam. — After Cuignard. 



may divide into two, a regular succession of changes in the 
arrangement of the materials composing it characterizing this 
process, which is commonly followed by the formation of a 
partition-wall separating the cell into two parts, each con- 
taining one of the daughter-nuclei. 



4 PLANT LIFE. 

7. Centrospheres. — The centrospheres are intimately re- 
lated to the nucleus. They are two very minute spherical 
bodies lying in contact with it (figs, i, 2). When the 
nucleus is about to divide one centrosphere goes to each 
pole (fig. 2, B), and the separation of the nuclear material 
occurs near the nuclear equator. Just as this occurs the 
centrospheres divide, forming a pair at each pole. Two 
accompany each daughter-nucleus. Their purpose is not 
yet fully understood. 



•••28 





Fig. 




Fig. 




Fig. 



t, showing its 



wall, and some 
il-drop. Mag- 



Fig. 3. — A cell from the interior of the leaf of the 
inclusions of the cytoplasm, z, the nucleus; c, chloropla 
nified about ioo diam —After Zimmermann. 

Fig. 4. — A, chloroplasts from the skin of the petiole of ivy; B, from the inner leaf- 
cells of morning-glory; C, from the same cells of Achyranthes. The shaded parts 
are protoplasm in which are embedded starch-granules, j, and proteid crystalloids, 
k. Magnified about iooo diam. — After Zimmermann. 

Fig. 5.- — Leucoplasts from a young shoot of Canna. The shaded part is protoplasm, 
in which are embedded starch-grains, s, and proteid crystalloids, k. Magnified 
about 1000 diam. — After Schimper. 



8. Plastids. — In most cells there are also other protoplas- 
mic structures, the plastids. In young cells these are small, 
rounded, colorless bodies. As the cell grows older they in- 
crease in size and number. At maturity, in cells which lie 
near the surface of green plants, they are commonly roundish 
or biscuit-shaped, of spongy texture, and colored yellowish- 



IN TROD UC TION. 5 

green by a substance known as chlorophyll. These are con- 
sequently known as chloroplasts or chlorophyll-bodies (figs. 
3, 4). In other cells, particularly those for the storage of 
food, they may develop into smaller, denser, flattened or 
roundish, uncolored bodies, called leucoplasls (figs. 5, 6, 7). 
These may act either as starch-accumulators, or in case 




Fig. 6. 



Fig. 7. 



Fig. 6.— Part of the cell-contents of an inner cell of white potato, z, nucleus; j, 
starch-grains, each having been formed by a leucoplast, /, which is still attached to 
one side of the grain; k, crystalloid. Magnified abont iooo diam. — After Zimmer- 
mann. 

Fig. 7.— Leucoplasts in place in a young cell of a leaf of vanilla. /, leucoplasts; z, 
nucleus; e, an oil-former or elaioplast. The unshaded spaces surrounded by proto- 
plasm are vacuoles. Magnified about 1000 diam. — After Wakker. 

of need, in young cells, may even be converted into chloro- 
plasts. In other cells, particularly in highly colored parts, 
the plastids may become of most diverse form and size, and 
colored red or yellow, whence they are called chromoplasts 
or color-bodies (figs. 8, 9). 

9. Wall. — The cell-wall is formed by the protoplasm. 
In green plants when first formed it consists chiefly of cell- 
ulose, with which, as it grows older, various other substances 
may be mixed. Some of these, such as pectin, are present 
even in the young wall, and may increase with age; others 



O PLANT LIFE. 

are characteristic of special changes which the wall may 
undergo. The most noticeable changes are four: (i) Some 
cell- walls contain suberin or cutin, fat-like substances by the 
presence of which water and gases are hindered from passing 




Fig. 8. Fig. 9. 

Fig. 8.— I, chromoplasts from flower-leaves of an orchid; II, from the root of carrot; 
III, from the fruit of mountain-ash. Embedded in the protoplasmic body of the 
chromoplast are sometimes proteid crystalloids, /, pigment-crystals, _/", or starch- 
grains, j. Magnified about 1000 diam. — After Schimper. 

Fig. 9. — Chromoplasts from the flesh-colored shoots of the horsetail, containing the 
coloring matter in the form of granules embedded in colorless protoplasm. Mag- 
nified 1400 diam. — After Zimmermann. 

through. The cell-walls of bottle-cork are suberized, and 
those in the skin of the apple are cutinized. (2) Some cell- 
walls are lignified, as, for example, those of wood by reason of 




Fig. io.— A part of a thin slice lengthwise through the centre of the stem of garden- 
balsam. The cells and vessels are elongated and are here seen from the side, show- 
ing the thickened lines on the side walls of v, v', v", v"\ v"", and v'"". Mag- 
nified about 400 diam. — After Duchartre. 

the presence of certain substances (vanillin, coniferin, etc.). 
They allow the ready passage of water and gases. (3) Others 
are so transformed that, in contact with water, they swell 
enormously, forming a mucilage or gum. These swelling 



INTRODUCTION. 



substances are produced by the alteration of the cellulose or 
other constituents of the original wall. (4) An excessive 
deposit of mineral matters in tin 
wall is known as mineralization 
Such walls may even retain their 
form after all organic matter is 
burned out, as in the skin of the 
scouring rush or horsetail. 

10. Growth of the cell-wall. — 
As the cells become older the wall 
may increase in thickness. It must 
also increase in area as the cells 
grow in size. The growth in area 
is usually accomplished by putting 
new particles between the older 
ones. Growth in thickness is rarely F 
uniform. When the wall grows 
thicker except at certain spots, these 
remain as pits or pores in the 
thickening layers. When only cer- 
tain spots or lines grow thicker, 

the wall shows projecting spikes, bands, or threads, which 
give it the appearance in figs. 10, n. 




c 11. — Cells from a liverwort 
showing thickened walls A, 
half an elater; A', a part more 
highly magnified; B, a cell from 
the lower part of the thallus, 
with reticulate thickenings 
(shaded); C, D, rhizoids with 
isolated branched thickenings. 
Highly magnified. — After 
Sachs. 



CHAPTER I. 



SINGLE-CELLED PLANTS AND COLONIES. 

In the lakes and pools, in ditches and slow streams, on 
the surface of damp rocks and wood, may be found many 
sorts of microscopic plants, whose entire body is merely a 
single cell. 

Blue-green algae. 

11. Fission-algse. — The simplest forms of these, the fission- 
algae, have the protoplasm only slightly differentiated. The 
central part becomes the nucleus, while the whole of the 
remaining protoplasm is colored by the chlorophyll and a 
blue coloring matter called phycocvanin, so that in mass these 
algae look bluish-green or even blackish. For this reason 
they are called blue-green algae to distinguish them from those 
in which only the yellow-green of chlorophyll is present. 

12. Gelatinous colonies. — The cell-wall may be a thin 
sheet of cellulose, but commonly it is 
composed of several layers, of which 
the outer are changed into mucilage. 
This swells into a transparent jelly 
when wet, either becoming homo- 
geneous or showing distinct stratifica- 
tion. When a number of such forms 
grow in company (fig. 12), this 
jelly-like material blends into a single 




plants seems to be em- 



Fig. 12— A blue-preen aljra 
(Gl(roca/>sa<. Single indi- 
viduals, A, and colonies 

\S' E) r °a va r ous wf s associated 

Magnified 300 diam. — After 

Sachs - bedded. 

13. Gelatinous filament-colonies. — In other cases, instead 
of being associated only by the adhesion of the mucilaginous 
portion of the cell-wall, the cells, still practically inde- 
pendent the one of the other, remain connected by the 



SINGLE-CELLED PLANTS AND COLONIES. 



firmer portions of the wall into rows, forming irregularly 
coiled or serpentine filaments, which are embedded in a 
profuse gelatinous material (fig. 13). The essential inde- 
pendence of the individual cells, even though they remain 
connected, is shown by the fact that such a chain may be 



) 8 





tKf? 



Fig. 13. — Nostoc. A. a gelatinous colony, irregularly lobed. Natural size. B, a 
portion of a serpentine filament with five heterocysts (one at each end by which it 
was separated from the rest of the cells composing the filament, and three inter- 
mediate ones) and the jelly belonging to it. Magnified about 400 diam. — After 
Thuret and Janczewski. 



broken up into any number of pieces and each piece will 
retain all its powers. Here and there in the chain there 
occur cells unlike the rest (Ji, fig. 14), called heterocysts, 
whose function seems to be to break the chain into pieces, 
from the growth of which independent colonies may arise. 
The association of considerable numbers of these plants in 
colonies gives rise to masses of jelly which vary from the size 
of a pin-head to 2-5 centimeters in diameter. They may be 
found adhering to water-weeds as clear- or dirty-green 
masses, or sometimes floating free (-/, fig. 13). 

14. Filaments of loose organization. — Of very near kin 
to these plants are the oscillarias, which have received this 
name from the pendulum-like swinging of their tips (fig. 15). 
In them the cells remain connected more extensively and 
more firmly, so that each is disk-shaped, and the filament is 
much less easily separated into its component cells. More- 



[O 



PLANT LIFE. 



over the gelatinous part of the wall is much less prominent, 
so that often it is only seen with difficulty. Even though 
invisible, it may be detected by the slippery feel of the 
plants when rubbed gently between the fingers. 





Fig. 15. 

Fig. 14. — Part of a filament ol A nab ana. h, heterocyst; a-d, successive stages in 
the division of a cell of the filament. Magnified 540 diam. — After Strasburger. 

Fig. 15. — Oscillaria. a, the tip; b, a portion of the middle of a filament. Magnified 
540 diam. — After Strasburger. 

15. Feeding habits. — The feeding habits of the oscil- 
larias are worth notice. They are found in permanent 
puddles and ditches where organic matter is decaying. The 
significance of this is that some of the ancestors of the green 
oscillarias probably had offspring which, instead of living 
upon food prepared by means of the green coloring matter 
(see ^[ 230), learned to utilize the organic matter in the 
water, at first perhaps no more than the present oscillarias 
do ; but gradually they came to live exclusively upon it. 
As a consequence, they lost their color and became incapable 
of existing where organic food cannot be had. 

Bacteria. 

16. Fission-fungi. — Along with the loss of color and 
change of habit went a diminution in size. They have thus 



SINGLE-CELLED PLANTS AND COLONIES. II 

become so different that they are now known as fission-fungi, 
and popularly as bacteria, bacilli, microbes, germs, etc. 
These plants, probably the descendants of common ancestors 
with the fission-algae, are the smallest known organisms 
(figs. 1 6, 17). The diameter of many sorts does not 



4?V 



VSf\ 


%|| 


gC 




© % 

Fig. 16. — Various bacteria, a, Micrococcus, the " blood-portent" ; i, zoogloea form 
of the same ; c. Bacterium aceti, the ferment of vinegar ; </, Sarcina, a harmless 
parasite of the human intestine, a, /', magnified 300 diam.; c, 2000 diam.; </, 800 
diam.— After Kerner. 

exceed .0005 of a millimeter. That would allow 175 to 
lie side by side upon the edge of the paper on which this 
book is printed. In many the successive divisions are 
parallel, in others they divide the cells in two planes, ami in 
others again in three. The cells, when they divide, separate 
readily, in most sorts never cohering at all, but living as 
independent cells as soon as produced. Other sorts remain 
connected into two- to several-celled chains, sheet, or packets 
(a, d, fig. 16). A few have their cells firmly coherent into 



PLANT LIFE. 



a filament. As the cells are either spherical or rod-like, the 
shape of the colony depends upon the shape of the compo- 
nent cells and the way in which they divide (see ^[ 24). 

17. Gelatin. — In the fission-fungi, as in the fission-algae, 
considerable masses of gelatinous material are produced, in 
which the cells may lie embedded. The films, sometimes 
smooth, sometimes wrinkled, which appear on an infusion of 
organic matter, are formed by the masses of bacteria which 
become embedded in the gelatinous material produced by 
the alteration of their cell-walls {b, fig. 16). 

18. Cilia. — Most species are furnished with locomotor 
organs consisting of fine threads of cytoplasm protruded 
through the wall, which, by their sudden contraction on one 
side, lash about like whips, and propel the cell by jerky, 
darting motions through the fluid in which it swims. These 
lashes, called cilia, may be single at the ends of the cell 
(C, fig. 17), or many at ends or sides (A, fig. 17), or the 

It * \\ 



Fig. 17. — Bacteria stained to show cilia. A, cilia tufted at one end; />', cilia irregu- 
larly distributed over body; C, cilium single at one or both ends. B. the bacillus 
of typhoid fever; C, the bacillus of Asiatic cholera. Magnified 775 diam.— After 
Migula. 

whole cell may be covered with them like hairs (B, fig. 17). 
They may be withdrawn or drop off when the plant comes 
to rest, as when they form the scums previously mentioned. 

These plants are most interesting on account of their 
economic relation to health and disease, decay, fermentation, 
etc., which cannot be discussed here.* 

* For further information on these plants, see Frank/and ; Our 
Secret Friends and Foes ; Prudden : Story of the Bacteria, Dust and 





SINGLE-CELLED PLANTS AND COLONIES. 



13 



Yellow-green algae. 
19. Single-celled plants with chloroplasts.— Among the 
single-celled green plants, one of the most common groups 






Fig. 18. — Pleurococcus viridis. A, a single individual; B, a colony shortly after 
division; C, the same after separation. Magnified 540 diam. — After Strasburger. 

is that represented by fig. 18, which shows a representative 
of an extensive series in which the vegetative body consists 
of a single cell with its wall, cyto- 
plasm, nucleus, and a few relatively 
large chloroplasts. In this greater 
specialization of the protoplasm, these 
plants show the only ■ advance upon 
the blue -green algae. The wall in 
such as this Pleurococcus is almost 
uniform and quite thin. 

20. Colonies. — The cells are fre- 
quently associated in 
bedded in jelly or not. The most 
striking and elaborate of these colo- 
nies is formed by Volvox (fig. 19). 

In this plant the colony is a hollow 
sphere, often large enough to be seen 
by the naked eye as a minute green ball, composed of thou- 
sands of individuals, embedded in a common jelly, arranged 
in a single layer at the surface. Each is connected with its 
immediate neighbors by strands of protoplasm, and two 

its Dangers, Drinking-water and Ice Supplies ; Russell: I 'airy Bacteri- 
ology; Frankel (tr. by Linsley) : Bacteriology (medical). 



1 • Fig. iq. — Volvox. 

colonies, em- - ni , individuals 



olony. 

repre- 
sented by the minute circles, 
between which the protoplas- 
mic strands form a network. 
The large balls in the interior 
are daughter-colonirs to be 
set free upon the rupture and 
death of the mother-colony. 
Magnified about 45 diam. — 
From Bessey. 



U 



PLANT LIFE. 



cilia are protruded into the water outside. The lashing of 
these rolls the whole colony about. Each vegetative in- 
dividual is entirely like the others, but those connected 
with reproduction become specialized. 

Diatoms and desmids. 
21. Shelled plants. — Other one-celled plants constitute a 
group known as diatoms, found in both fresh and salt waters, 
a b c d 




Fig. 20. — Various diatoms, a, Synedra ; 6, Pleurosigma : c, d, GrammatofiAora, 
side and top views ; c. colony of Gomfihonema, with branched stalks attached to an 
alga;y, g, single cells of same, more magnified, top and side views; A, colony of 
Diatoma, ihe cells connected into a zigzag band ; t, k, colony and individuals (top 
and side views) of Fragillaria : /, «/, >i, Cocconema. In m the pair is surrounded 
by jelly preliminary to the escape of the protoplasm and the formation of two new 
cells (auxosporesi which has been completed in «.— After Kerner. 

either attached or free-swimming (figs. 20, 21). The dia- 
toms are very various in form, and present two different 
aspects. When seen from the side they are generally elon- 
gated-rectangular. When looked at from above they are 
short-cylindric, disk -shaped, boat -shaped, or variously curved 



S1XGLE-CELLED PLANTS AND COLONIES. 15 

or angular. They are peculiar in having the cell-wall so im- 
pregnated with silica that scarcely any organic matter is left. 
Indeed the plants may be heated to a red heat and boiled in 
acid without destroying the form and markings of the cell- 
wall, so completely has it become silicified. To permit 
growth this rigid cell-wall is constructed in two pieces which 
fit together like the two parts of a pill-box (fig. 21). Each 
of these pieces, or valves, is sculptured into regular patterns 
in lines and dots, which are often so excessively minute or 
close together as to be barely visible with the highest powers 
of the microscope (b> fig. 20). Seen in mass, as they may 
often be on the sides of a glass aquarium, living diatoms 
appear yellowish-brown. The chloroplasts, which are some- 
times single and always few, contain a brownish pigment 
(dia/omin) in addition to the green chlorophyll. 




Fig. 2i. — A single diatom (Navicula amphirhynchus). A } top view ; />, side view, 
showing overlapping of the valves. The parts shaded by lines are the chloroplasts; 
the dotted part the protoplasm, with nucleus about the center of cell. Magnified 
750 diam. — After Pfitzer. 

It is not uncommon for the diatoms to form colonies by 
the adhesion of several or many individuals by means of 
gelatinous cell-walls. These colonies are ribbon-like, or zig- 
zag chains, or even branched filaments (//, i, fig. 20). 
Other sorts may be attached singly or in clusters by a gelati- 
nous stalk (e, fig. 20). In all cases the jelly, like the rest 
of the cell-wall, is a product of the protoplasm. The slow 



[6 



PLANT LIFE. 



gliding movements of some free diatoms are due to the pro- 
trusion of strands of cytoplasm through slits in the valves. 

22. The desmids. — These form another group of one- 
celled green alga;. They have neither the brownish color 
nor siliceous wall characteristic of diatoms, but are bright 
green cells of remarkably diverse and often beautiful forms. 
As a rule the cell is flattened and is divided almost into two 
by a deep constriction near the middle (a, b, c, e, fig. 22). 




Fig. 22. — Various desmids. a, Micrasterias ; 6, Cosmarium ; c, Xanthidium ; 
d, Closterium ; f, Staurastrum ; J, Aptogonum. Magnified about 200 diam. 
— After Kerncr. 



Often the body of the cell is covered with warts or spine-like 
projections (b, c, fig. 22), or is prolonged into horn-like or 
hair-like lobes. These plants also frequently cohere into 
colonies (_/", fig. 22). In that case tooth-like projections of 
the cell-wall may interlock. 



CHAPTER II. 

LINEAR AND SUPERFICIAL AGGREGATES. 



Obviously some of the plants mentioned in the last chapter, 
such as the oscillarias, are colonies of cells well on the way 
to complete union into coherent filaments whose elements are 
attached to each other by considerable areas of the cell-wall. 
In order clearly to understand this condition, we must con- 
sider the mode of origin of the individual cells composing 
the row. 

23. Fission. — Under conditions unknown to us, in the 
course of its growth a cell may divide by a process known 




Fig. 22A. — A, one of the final stages in cell-division. The daughter-nuclei are still 
connected by kinoplasmic filaments, and across the equatorial plane particles of new 
cell-wall material are formed. A', the completion of cell-division; the daughter- 
nuclei have rounded off and the new wall is like the lateral walls. Magnified 880 
diam. — After Strasburger. 






Fig 22B.— Three stages of division in the same cell of an orchid (£pipactis 
palustris). The cell is occupied in great part by vacuoles, [n this case the new 
wall forms first on one side between tin- nuclei (.! ), which gradually travel across 

to the opposite side (A), the wall extending until it is complete (O. Magnified 
about 380 diam. — After Treub. 

17 



1 8 PLANT LIFE. 

as fission. The material of the nucleus passes through a 
complex series of changes and separates into two parts. In a 
plane between these daughter-nuclei particles are deposited 
to form a cell- wall (A, fig. 22A). The formation of the 
partition-wall may occur simultaneously in all parts, or it may 
be formed on one side first and the nuclei move across the 
cell until it joins the lateral walls (fig. 22B). In this way an 
isolated unicellular plant of Pleurococcus (A, fig. 18) may 
divide into two cells so that it consists of two hemispherical 
cells, each capable of independent growth (fig. 23, A). 
After a time these cells may separate from each other by the 
cracking of the original wall at the line of juncture with the 
new partition and the cleaving of this partition parallel to its 
surfaces into two layers, one of which covers a portion of 
each of the thus disconnected cells (fig. 18, C). If this 
process of division and separation goes on, the result will be 
the production of a number of independent cells more or less 
closely associated but not connected. 

24. Cell-rows, surfaces, and masses. — In many cases, 
however, a second division occurs in one or both cells before 




Fig. 23.— Diagrams of cell division. A, division of a spherical cell into two hemi- 
spherical cells, a, b, by the wall i. />', the same after further division in planes 2, 
2, 3, parallel to 1. a has divided by wall 2 into a' and another cell which has again 
divided by wall 3 into a", a", b has divided into i', b' , the inner of which has 
elongated preparatory to a division into b", b" , as by wall 3. C, fig. A after a 
second division, by wall 2, at right angles to 1. 

separation; and sometimes even a third division takes place. 
It is evident that the position of the later partitions deter- 
mines the form of this temporary aggregate of cells, (a) If 
each of the two divides in a plane parallel to the first parti- 



LINEAR AND SUPERFICIAL AGGREGATES. 1 9 

tion, a roiv of four cells will result; the two inner cells 
would be disks or short cylinders, while the two outer would 
be hemispheres (fig. 23, B). (b) But if (as is actually the 
case in Pleurococcus, B, fig. 18) the new partitions are at 
right angles with the first, the result is a cluster of four cells, 
each of which is a quarter of a sphere (fig. 23, C). 

Should a third division occur, it is conceivable that the 
new septa might be placed parallel to those already formed, 
in case a ; or parallel to one set and at right angles with 
the other, in case b ; or at right angles to both, in case c. 
In the first instance there would be formed a row, or filament, 
of eight cells; in the second, a sheet of eight cells; or, in the 
third, a mass of eight cells. This exhausts the possibilities in 
the position of successive partitions. If other divisions 
occur, they will necessarily be more or less nearly parallel to 
some one of the first three sets.* 

The structures resulting from cell-division where the cells 
remain united are conveniently designated as follows: (1) 
cell-rows, filaments, or linear aggregates, arising by division 
in one plane; (2) cell-surfaces, or superficial aggregates, 
arising by division in two planes; (3) cell-masses, or solid 
aggregates, arising by division in three planes. 

It is manifest that there are likely to be all degrees of union 
remaining between the cells of linear and superficial aggre- 
gates, and that the extent and firmness of such union will 
depend largely upon the character of the wall. As in every 
other case, the artificial distinction between cell-colonies and 
cell -aggregates is bridged by all manner of intermediate 
forms. 

Filamentous algae. 

There is a large number of plants in which the vegetative 
body throughout life has the form of a filament. The green 
*The formation of partitions at angles other than 90 or l8o° to pre- 
ceding ones would not affect the genera] result, luu would only render 
the form of the product, as well as of the individual cells, less regular. 



20 



PLANT LIFE. 



plants of this sort live almost entirely in water or in wet 
places, and may be conveniently designated as the filamentous 
algce. 

25. Spirogyra, etc. — Among these none are more beautiful 
or interesting than the filamentous Conjugate, represented in 





Fig. 26. 

Fig. 24. — A cell from filament of Sfirogyr-a. 

ch, chloroplast (there are three in this Veil); 

/, pyrenoids ; k, nucleus. Magnified 200 

diam. — After Straslmrgcr. 
Kig. 25. — A cell from filament of Zygnema, 

showing two stellate chloroplasts, in each of 

which is a pyrenoid, with the nucleus between 

them. Cytoplasm poorly shown. Magnified 

550 diam. — After Sachs. 
Fig. 26. — Two cells from filament of Zygonema, 

showing the gelatinous sheath greatly swollen. 

Magnified 245 diam. — After Klebs. 



our waters by the genera, Spirogyra, Zygnema, Mesocarpus, 
and some others.* They may be readily recognized, during 
their vegetative period, by their unbranched filaments, bright 

*To the Conjugate also belong tbe single-celled desraids already 
described. 



LINEAR AND SUPERFICIAL AGGREGATES- 21 



green color, and slippery " feel ' ' between the fingers.* Under 
the microscope, they are at once distinguished from other 
filamentous algse by the shape of their 
chloroplasts. In Spirogyra these form 
one or more fiattish, spirally wound rib- 
bons, notched on the edges, and embedded 
in the protoplasm near the cell-wall (ch, 
fig. 24). In Zygnema there are generally 
two irregularly star-shaped chloroplasts 
(figs. 25, 26) ; while in Mesocarpus a 
single flat, plate-like chloroplast, nearly 
as wide as the cell, traverses its center 
(ng- 27). f 

Embedded in the chloroplasts of these 
and other algaj are usually seen one or 
more angular, colorless bodies, often sur- 
rounded by a jacket of starch. These are 
crystals of reserve proteid, known aspyre- 
noids (/>, figs. 24, 27). Their size depends 
upon the amount of reserve food possessed 
by .the plant. 

In these plants there is little or no dif- 
ference between the parts of the filaments. 
If broken into two, each part may continue 
growing with no damage to any part 
except the cells which were ruptured in 
severing the plant. 

26. Ulothrix, etc. — But other filamentous alga? show a 
distinction between base and apex. In Ulothrix (fig. 301) 

* This slipperiness is due to the gelatinous outer part of the cell-wall 
(fig. 26), which is only visihle after special treatment or on examining the 
filaments in a thin mechanical solution of Chinese ink. 

f See also Ulothrix (tig. ?oi), which has in each cell a single chloro- 
plast in the form of a thick ring. 




ig. 27.— A cell from fila- 
ment of Mesocarpus. 
The darker body nearly 
filling cell is the chloro- 
plasl (lace view) in 
which are pyrenoids, /, 
and tannin vesicles, g. 
1 f seen from a direction 
at right angles it would 
appear as a narrow 
stripe in the center of 
the cell, z, the nucleus. 
Magnified about 200 
diam.— After Zimmer- 



22 



PLANT LIFE. 



the basal cell is elongated and pointed, and is colorless, 
because it is not furnished with chloroplasts like the others. 
By this pointed cell the plant is loosely attached, at least 
when young, to the substratum, while the green portion 
waves freely in the water. Thus arises a distinction into two 
parts, viz., the rhizoid and the thallus. 

In Cladophora, Vaucheria, and their allies, the plants are 
generally attached by a well-developed rhizoid-region, which 
is often branched {w, fig. 28), as is also the thallus. In 




iture 



Fig. 28. — A young plant of I'aucheria, developing from the spore. A, 

:int further develop 
ch it attaches itsel 

next the wall on all sides 



spore ; B, the same after germination has begun ; (', plant further developed from 

hich it attaches itself to the 



spore, s/>, with growing apex, j, and rhizoid, iv, by 
mud. The chloroplasts are numerous and close togetl 
Magnified 28 diam.— After Sachs. 



contrast with the preceding, therefore, localization of grmvth, 
producing branching, may be observed. 

27. Branching. — A branch begins by the growth in area 
of a limited portion of the cell-wall. The pressure of the 
contained protoplasm upon the wall causes it to bulge out- 
ward at this point, and the convexity gradually increases as 
the region grows until the swelling becomes an outgrowth, 
whose further lengthening constitutes a branch similar to the 
main filament. Growth in length may be limited to the tip 
of the filament, or to a narrow zone including one or more 
cells, or it may occur indifferently in any part. 

28. Coenocytes. — Many algse, while externally like others, 
which are divided into true cells, have not the units of 



LI X EAR AND SUPERFICIAL AGGREGATES. 2$ 

structure separated by cell-walls. In Vaucheria, for example, 
the whole of the vegetative body forms a single chamber, 
in which lies the united protoplasm, corre- 
sponding to many cells, as shown by the 
numerous nuclei which are distributed through 
it. The external walls of the cells are formed, 
but, when the nuclei divide as growth proceeds, 
the protoplasm does not divide, and the septa 
or partition- walls are not formed. Such an un- 
septate company of cells is called a ccenocyle. 

In the cladophoras (fig. 29) some of the 
normal divisions are complete, while others 
are only nuclear divisions. Consequently the 
cladophoras seem to be a filament of true 
cells, but in reality each apparent cell is a 
ccenocyte, as shown by the several nuclei in 
each (fig. 30). 

29. External segmentation. — A plant 
body of this construction may attain con- 
siderable size and complexity, as in Caalerpa 
(fig. 31 ) and Acetabularia (fig. 32),* even to 
mimicking, upon a small scale, the form of 
leafy plants. In such cases the external walls 
become considerably thickened, and across V,G a 9— a single 

J plant of Clado- 

the protoplasm and its large vacuoles, from Mora, showing 

profuse monopo- 

one side of the chamber to the other, run <iial branching. 

Natural size. — 

irregular bars of cellulose which act as braces AfUr Hauck. 
to prevent the collapse of the outer walls (fig. ^^). 

In Caulerpa, particularly, a high degree of development 
as to external form is reached (fig. 31 ). There is a stem- 
like axis, v-s, creeping in the mud, which bears green leaf- 
like branches, b, on one side and clusters of colorless root- 



Note carefully the scale of the figures. 



24 



PLANT LIFE. 





Fig. 31. 
Fig. 30. — One ccenocyte from a branch of Cladophora, shi 

chloroplasts ; /;, pyrenoids ; a, starch-grains; «, nuclei. 

After Strasburger. 
Fig. 31 — Part of a plant of Caulerpa. See text, r 29. Two-thirds natural size. 

—After Sachs. 



i-ing fifteen nuclei, ch. 
Magnified 270 diam. — 




Fig. 32. — Acetabular ia. A, an entire plant, natural size —After Woronin. A, dia- 
grammatic longitudinal sec linn through the upper end of the stalk and the um- 
brella-like circle of crowded branches which grow together ; «, scars left by fall of 
an earlier whorl of short branches ; r, w, rudimentary branches ; C, the base of 
stalk showing rhizoids for attachment, _/", and for storage, b. Magnified 20 diam. — 
After De Bary and Strasburger. 



LINEAR AND SUPERFICIAL AGGREGATES. 2$ 



a I >ase 
shable, 



like branches, w, on the other. Not only are 

(posterior end) and an apex (anterior end) distingu 

but the plant shows a difference between 

an upper (dorsal) and under (ventral) 

side, the leaf-like thallus lobes arising 

from the dorsal side, while rhizoids 

spring from the ventral side. 

30. The thallus. — To the loose 

aggregation Of Single Cells into Colonies Fig. 33. - Transverse section 

c j c . - ., ... of axis of Caulerpa, show- 

Ot definite form, as well as tO the body ing cross-bars to stiffen wall. 

r lii- • ■ • Magnified about 25 diam. — 

formed by their more intimate union After Murray. 
in the linear and superficial aggregates just described, the 
name thallus is applied. The term is most frequently applied 
to those more complicated forms which constitute the vege- 
tative bodies of the higher algai, which are now to be 
described. 




CHAPTER III. 



THE THALLUS OF THE HIGHER ALG^E. 



31. From linear to solid aggregates. — From the fila- 
mentous algae, whose body is a linear aggregate of cells, it is 
but a step to those forms whose body is a superficial aggre- 
gate. When JMonostroma grows from the single cell as which 
it begins life, the cell-divisions, instead of occurring succes- 
sively in parallel planes, are made in two planes at right 
angles to each other. The result is a single sheet of cells 
forming a leaf-like thallus attached to stones or other algae. 
The broader forms are sometimes 20-25 cm - w hlc. 

Ulva, a near relative, develops in much the same way, 
but at least one series of divisions occurs in a third plane, at 
right angles to the other two, so 
that the body of the sea-lettuce con- 
sists of two layers of cells. As 
fig. 34 shows, it is very clearly dif- 
ferentiated into rhizoid and thallus. 
If two such layers separate from 
each other, as they do in Entero- 
morpha, a hollow, sac -like body is 
formed. 

So, from the linear aggregates, 
we pass through superficial to solid 
aggregates of a broadly extended 
form. 

The transition from linear to solid aggregates of slender 

26 




Fig. 34. — A small plant of Ulva 
lactut a. the sea lettuce, show- 
ing thallus, and rhiz..id for 
attaching it to rocks. Natural 
size. — From Bessey. 



THE THALLUS OF THE HIGHER ALGSE. 2J 

form may be understood by comparing with one of the fila- 
mentous algas a member of an isolated order of green fresh- 
water algre, the CharacecB. 

Characeae. 

32. The order. — These plants constitute an outlying group 
of considerable antiquity, having no near relatives living, yet 
showing in the vegetative body some structural resemblance 
to the filamentous algre, while, as a whole, their external 
form imitates quite closely that of the higher plants (figs. 
35, 36). The species of Chara and Nitella (the two genera 
which make up the bulk of this order) are found in almost 
every temperate region, growing in dense masses submerged 
and rooting in the mud in quiet waters. They reach a height 
of 10-75 cm - 

33. External form. — The plants agree in having a central 
axis, at certain points of which * arise lateral outgrowths of 
two kinds. One kind forms a circle of branches, nearly like 
the main axis, except that their growth is limited. These 
themselves bear branches of simpler structure. The primary 
whorled branches are the so-called " leaves," and the second- 
ary ones which these bear are the so-called " leaflets." 

Just above one of the "leaves" in each whorl is pro- 
duced a branch precisely like the main axis, which has, like 
it, unlimited growth. 

34. The main axis. — In Nitella the axis consists of alter- 
nately long and short cells, a very short cell occurring at each 
point (" node") where branching occurs. The long cell 
extends from one " node " to another. This " internodal" 

* Commonly called nodes, and the intervals internodes. These terms, 
imposed from analogies with the seed-plants, are entirely misleading from 
a morphological point of view, as are also the names " leaves " and 
" leaflets," applied to certain divisions of the axis, hut they have heroine 
so fixed that it is difficult to avoid their use. 



28 



PLANT LIFE. 




F,G - 35.— Upper part of a Dlani .,{ ri v. 

Krou-.h (''leaves";, and a, li;^, 1,1 '/''.' ;;;:; ] , s ':'. w . l,1 < "honied branches of limited 
lowest being cut off. The small |„ ( |j, ' In ' ™ ncl,, ' s .." f unlimited growth, the 
organs. Natural sire -After wtle C ' eaVes are ,eafl «* " and sex- 



THE THALLUS OF THE HIGHER ALGM. 2Cj 

cell is, therefore, of an extraordinary length, as well as of 
large diameter. 




Fig. 36. — Upper part of a plant of Nitella. Natural 



30 



PLANT LIFE. 



35. Cortex. — Nitella and Chara are much alike, except 
that in Chara the main axis and all its brandies are com posed 
of a row of large cells, surrounded by a jacket of smaller ones 
(fig. 37). The walls of these outer cells are often much 
thickened, and incrusted with salts of lime to such an cxtmt 
as to render the axis very brittle. Around the main axis the 
cell-jacket is of much complexity ; it becomes more simple 




■<>x 




Fig. 37. 



Fig. 38. 



Fig. 37.— Transverse section of the axis of Chara. a, internodal cell; b, cortical cells 
Magnified about 30 diam. — From a drawing by C. E. Allen. 

Fig. 38. — Longitudinal section of apex of axis of Chara. x, apical cell. The seg- 
ment next below will divide into a nodal and an internodal cell ; the next one has 
already divided and the nodal half has again divided into two internal and several 
external (only •.; show) nodal cells. <-, </, internodal cells ; between them a node pro- 
ducing the branches (" leaves ") e and/; and the cortical branches a, a. 6, a similar 
branch growing up from node below, only its tip showing. Magnilied 330 diam. — 
After Sai hs. 



upon the whorled branches, and is wanting upon the ultimate 
divisions. 

While a cross-section of the axis shows a complete union 
between the walls of the cortical cells (b, fig. 37) and the 
central one (a, fig. 37), a study of their development shows 
that they are originally branches of the outer cells at each 
node, which likewise produce the circle of "leaves." The 



THE THALLUS OF THE HIGHER ALGM. 3 1 

branches from the node above grow downward and others 
from the node below grow upward until they meet and inter- 
lock about the middle of the internode (fig. 38). Thus, the 
cortical cells are not produced by division from the large 
central cell which they cover and stiffen, but simply grow over 
it and become united with it at a very early age, increasing 
with its growth and undergoing division at the same time, so 
that each cortical branch becomes multicellular. 

36. Apical cell. — The axis and all its branches, in both 
genera, are produced by the growth of a single apical cell of 
hemispherical form (x, fig. 38). The segments, successively 
cut off by partition-walls from its base, each divide a second 
time. One of the cells so produced increases rapidly in size, 
and becomes the internodal cell, while the other, by succes- 
sive divisions and differentiation, forms the node and its ap- 
pendages. In those branches which show unlimited growth 
the apical cell retains its hemispherical form until death ; but 
in the divisions with limited growth ("leaves") it becomes 
pointed and ceases to cut off segments from the base. 

37. Rhizoids. — -The structures by which the Characeos are 
held in place are adapted to penetrate the soft mud of the 
ponds and lakes in which they grow. From the nodes near 
the base of the axis arise numerous colorless rhizoids, often 
of considerable strength through thickening of the cell-walls. 

The thallus shows decided increase in specialization of 
members. This is accomplished, however, with a minimum 
of differentiation in the cells of which the body is composed. 

Polysiphonia. 

In the marine alga? a still higher specialization of members 
is reached. One of the red seaweeds may be used to show 
the gradual advance in complexity. 

38. External form. — The body oi Polysiphonia, a branch- 
ing alga (fig. 39) which grows in abundance upon rocky 



32 



PLANT LIFE. 



seacoasts, is not divided into nodes and internodes, and the 
branches are differently arranged from those of Chara. The 
^ axis is made up in its larger parts of five or 

more rows of cells, the central or axial row 
being surrounded by a jacket of at least four 
> others (fig. 40). But these originate by 
f i division from the central one, and are not, as 
' $ in Chara, merely adherent to it. It is, how- 
Yf ever, only in the larger parts of the axis that 





Fig 



Fig. 39.— An entire plant of Polysiphonia, showing mode of branching. Natural 

size. — After Kutzing. (See fig. 229.) 
Fig. 40. — Transverse section of one of the branches of Polysiphonia, showing a 

minute central cell with four large and four small cells surrounding it. Magnified 

about 50 diam. — From a drawing by Mr. Grant Smith. 
Fig. 41. — Apex of a branch of Polysiphonia which has nearly ceased growing. 

Magnified about 100 diam. — From a drawing by Miss Rowan. 

this structure appears ; at the tips even of the main axis the 
body is a linear aggregate (fig. 41). Polysiphonia, there- 
fore, may be looked upon as one of the simplest forms of a 
solid aggregate. 

39. Apical cell. — As in Chara, growth in length is quite 
definitely localized, because it is the elongated terminal cell 
of either the main or secondary axes (fig. 41) which pro- 
duces, by division near its base, the new cells whose subse- 
quent enlargement and division give rise to the axis. In 
some red algae the chambers are not cells but ccenocytes, as 
shown by the several nuclei. 

40. Color. — -In this plant, as in very many of the marine 



THE THALLUS OF THE HIGHER ALGM. 



33 



alga;, there exists, in addition to the green of the chloro- 
plasts, a special coloring matter, called phycoerythrin. To 
the naked eye, this color overpowers the green and gives the 




Fig. 42. — Upper part of a plant of Fucus Tesieulosus. r, midrib of thallus ; /, 
bladders; s, swollen tips covered by numerous elevations, in each of which is a pit 
(conceptacle) which contains many sex-organs. Two thirds natural size. — After 

Luerssen. 

plant a pink tinge. In other red algai it is often present in 
greater quantity and variety of hue, so that brilliant reds and 



54 



PLANT LIFE. 



purples, with shadings of brown and green, mark the more 
striking species. 

Fucus. 

From the very simple body of Polysiphonia to the common 
bladder-wrack, or Fucus vesiculosus, there are all stages of 
complexity, which cannot be traced here. 

41. External form. — The body of Fucus (fig. 42), is 
large as compared with the plants previously described. It 
is often 75-100 cm. long by 1-2 cm. broad, of greenish - 




Fig. 43. — A transverse section of the thallus of Fucus, showing midrib, r ; cortex, c ; 
medulla, m ; and a hair-pit,/. Magnified 10 diam. — From a drawing by Mr. C. E. 
Allen. 

brown color and cartilaginous consistency. Near the base 
the thallus is contracted into a stalk whose extremity is 
broadened into a sucker-like disk (often lobed) which at- 
taches the plant firmly to the wave- 
washed rocks on which it grows. 
Above, the thallus is flattened, with 
a thicker rib in the middle (fig. 
43), and branches abundantly by 
forking. These branches, though 
often twisted, really lie in the same 
place as the flattening. Here and 
there the axis shows pairs of oval 
f.g 44 -a longitudinal section swellings, the bladders, which, by 
$Zl?£ e nt?lp S T*l the contained gases, give greater 

flattened sides oJ e body t/ ,ap,cal buoyancy tQ the pl ant s in the Water. 

SWrfiSW&WE 42 - A P ical cell.-An examina- 
toiiii^ifiESdiSS! tion of the structure of the thallus 
-After Rostafinsk,. shows a decided differentiation of 

cells, which would be expected from the large and complex 




THE THALLUS OF THE HIGHER ALG&. 35 

form. At the apex of any growing branch is found a cluster 
of angular cells, thin-walled, of nearly uniform size, with 
abundant protoplasmic contents, and all in close contact. 
( >ne of these cells, lying in the center of the group, some- 
what larger and of different shape from the rest {c, fig. 
44), is constantly undergoing division, and thus cutting off 
cells (segments) from its two inner faces (1, 2, 3, fig. 44). 
The cells so produced undergo further divisions, forming 
thereby all the cells of which the thallus is composed. This 
group of dividing cells is present in all the higher plants. 
It constitutes the " growing point " or, better, the apical (or 
primary) merislem. The single cell from which all proceed 
in Fucus is called the initial, or apical, cell. 

43. Differentiation of cells. — But if a thin section of the 
thallus, from an older part, be examined (fig. 45), its cells 
will be found very different from those 
at the apex. The cells nearer the sur- 
face are smaller and of different form 
from those in the interior. They are 
also close-set, whereas those in the in- 
terior are no longer in contact with each 
other on all sides, but have been sep- **=> ^5^^^> 
aratec l>v the ^rowim: oi branches from ^.i,,/.,*^. ■..-»• «••« ■• 

J . ?. , f fe ,. rp , ummmmm 

the cortical cells between them. 1 hese 

Fi<;. 45— Diagram of a por- 

filamentous branches are crossed and in- tion of fig. 44 , magnified 

about 70 clum 1 cortex: 

terlaced, with wide intercellular spaces, w, medulla. Thevaried 

forms of the cells are due 

All of these older cells have enlarged, to the different planes in 

. . which the filaments are 

and, instead Ol being Idled With protO- cut. The clear spaces are 

filled with mucilage pro- 

plasm, they will be found to have large duced by the ceff-waiis. 

From a drawing by Mr. 

vacuoles and heterogeneous contents. C. E. Allen. 
The walls, also, are no longer thin and homogeneous, but 
have become thickened and differentiated into at least two 
layers, the outer of which is capable of swelling enormously 
in water, while the inner layer retains its usual form. There 




36 



PLANT LITE. 



arises thus a cortex, as the outer dense part is called, and a 
medulla or pith, as the mucilaginous and apparently isolated 
central cells and filaments are called. At the bladders, the 
pith becomes filled with air and other gases. 

44. Special functions. — Complete examination of all parts, 
the disk of attachment, the bladders, and the hair-pits (fig. 




Fig. 46. — Several plants of Lessonia, showing tree-like thallus and branched rhizoids 
attaching the plants to rocks, j B natural size.— After I .<• Maout & Decaisne. 

43) with which many species are covered, would reveal still 
other modes of differentiation of cells from those of the 
apical meristem. Accompanying the change of form is 
always specialization of function, which we can interpret 
only in a very imperfect fashion from our own standpoint. 



THE THALLUS OF THE HIGHER ALGJE. 



37 



The compact small cells forming the surface are nutritive 
and probably in part protective ; the bladders serve to in- 
crease the buoyancy of the plants when the tide is in ; while 
the abundant mucilage, formed in the interior from the cell- 
walls, serves to retain the moisture when the plants are ex- 




showing differentiation of thallus. Natural size. — 
After !■< nnett >v Murray. 

posed by the ebbing tide ; the hair-pits are functionless, so 
far as known ; and the strong, elastic cells of the disk and 
stalk above hold the plants in place as they sway constantly 
back and forth in every wave of the rising or falling tide. 

45. Color. — The coloring matter in the chloroplasts of 
Fucus and other brown seaweeds is chlorophyll (green) and 



3$ PLANT- LIFE. 

phycophoein (brown). The chloroplasts exist chiefly in the 
cortex, which is, therefore, the food-making tissue (see ■" 230), 
while the internal tissues are used for storage of reserve food. 

46. Intercalary zones of growth. — Some of the brown 
seaweeds, instead of growing at the tip, grow in a zone at 
the base of the flatter part of the thallus, just above the round 
stalk. Such growth is called intercalary growth. There can 
be no single initial cell, but at least a zone of initials. 

Some species grow to great lengths. One Australian species 
is said to attain a length of 200-300 meters. Still others 
have the form of a tree, the stalk-like portion representing 
the trunk, with a crown of flattened, frond-like branches 
above (fig. 46). 

The thallus in the "gulf-weed," or " sea-grape "* (fig. 
47), is still further differentiated into rounded, stem-like parts 
and flattened, leaf-like ones. The bladders are berry-like 
enlargements in the middle of short, rounded branches, and 
the form is strikingly like that of a small herb. 

* This plant is of interest, also, because from its scientific name, Sar- 
gassum, is derived the name of that region in the North Atlantic, in the 
loop of the Gulf Stream, the Sargasso Sea, where the plants accumulate 
after being torn off the tropical shores on which various species grow. 



CHAPTER IV. 

THE FUNGUS BODY OF HYPHAL ELEMENTS. 

Fungi. 

Fungi are plants without chlorophyll, whose body is gen- 
erally made up of long filaments, either loosely or densely 
interwoven and united. 

47. Origin. — As the bacteria, the smallest and simplest 
plants, were derived from the lowest algae by slow adaptation 
to a different kind of food, so, at various points in the 
ascending scale of algal life, certain algae have adapted them- 
selves to the use of organic food which they could secure 
ready-made. These, having no use for the chlorophyll and 
chloroplasts, have gradually lost them. The adoption of the 
habit has proved highly successful, both among the simple 
bacteria and the more highly organized true fungi. The 
ancestors of the present species were — how long ago no one 
can say — probably at first chiefly, if not exclusively, aquatic. 
Some, at the present time, have the same habit, growing in 
infusions of organic matter. Others attach themselves to dead 
or even living animals or plants in the water. The soil (con- 
taining in its upper layers more or less organic matter from 
the offal of plants and animals, or from their dead bodies) 
and dead or living organisms furnish places of growth for a 
great number of species which have adapted themselves to 
other than aquatic life. 

48. Hyphae.— The filaments of which the fungus body is 

39 



40 PLANT LIFE. 

composed are called hyphne. Each is the result of growth 
from a single cell, and is comparable to the thread-like body 
of the filamentous algae. 

There is, naturally, a great variety in the hyphas of differ- 
ent species of fungi. Some are relatively large ; others very 
small ; some of even diameter and caliber, others irregular 
and with unequally thickened walls ; some very thin-walled, 
others very thick -walled. Between these extremes is to be 
found a complete gradation. 

They grow in length at the apex only. In many kinds 
partitions are formed at more or less regular intervals, as the 
growth in length proceeds. In others no partition-walls are 
formed, though division of the nucleus takes place. Even 
when transverse partitions are formed, they do not separate 
the filaments into cells, but each chamber, or sometimes the 
whole filament, is a coenocyte. 

49. Branching. — As the hyphos elongate, branching may 
occur. If a branch is to be formed, a limited area of the cell- 
wall begins to grow more rapidly than the rest. This allows 
a slight bulging of the growing region; 
the swelling increases and soon takes 
the form of a branch, like the main 
axis. It may remain short or continue 
to grow indefinitely in length. Com- 
monly a septum is formed at the base 
of the branch. If such a branch arises 
first as a minute pimple, so that it 
remains connected with the parent axis 

Beer-yeast(Sacc/taro- . 

cerevisi.r). «, a full- by a small neck, and has only limited 

crown plant with a branch ... 

'lhii(l) partially developed. /', growth 111 length, it IS Called a blld 

r, colonies formed by budding, 

the individuals still attached, and the process is known as budding 

Magnified 750 diam.-Aftcr ,. ox e , . , ,, 

Reess. (fig. 48). Such branches are usually 

easily broken off, thus readily producing independent plants. 
(See further under Reproduction, * 302.) In some species of 




THE FUNGUS BODY OF HYPHAL ELEMENTS. 4 1 

fungi, profuse branching is the rule; in others, the branches 
are few. 

50. Mycelium. — When branching is profuse, or when a 
considerable number of individuals grow near together, the 
filaments often become interwoven and entangled in so com- 




Fic. 4g.— A single plant of Mucor Mucedo, showing the mycelium as it developed 
from a single spore in an infusion of dung. It bears a single erect reproductive 

branch rising above the fluid. Magnified .•■■, diam. Afler Urcteld. 



plex a web that it is impossible to follow a single hypha for 
any distance. Such a mat of hyphse is called a mycelium, 
a term which is also used to designate the vegetative hypha? 
collectively, whether forming a felted mass or not (figs. 49, 
50). The mycelium may be formed wholly upon the sur- 



42 



PLANT LIFE. 



face of the object upon which t he fungus lives; or parts of 
it may be superficial, and part may penetrate that object ; or 
all of it may be hidden within the substratum.* In some of 
the common molds (Mucorini), the cobwebby threads lying 
upon the surface of the substratum constitute the exposed 
part of the mycelium, while other hyphae penetrate deeper ; 

K 




Fig. 50. — A section of part of the aerial body of Polyporus. s/>, hyphae running at an 
angle to the section, cut across ; A", crystals of oxalate of lime. Magnified about 
500 diam. Attn Vogl. 

in others (Penicillium, etc.), the superficial hypha? become 
so interwoven that they may be lifted off the substratum (as 
from jellies, jams, syrups, etc.) as a coherent layer. But in 
most cases, especially when the fungus grows on a solid 
medium, the hyphae become adherent to it and permeate it 
SO that they cannot be separated from it, even by the most 
careful dissection. 

* This non-committal term may be used to designate the material upon 
which the vegetative part of the fungus grows, whether it be a living 
body, a dead organism, or organic matter in solid or liquid form. 



THE FUNGUS BODY OF HYPHAL ELEMENTS. 43 

51. Parasites. — Especially is this true of those fungi which 
grow in the interior of living organisms. The higher plants 
are liable to be fastened upon by parasitic fungi, and com- 
pel led to act as hosts to their unbidden and unwelcome guests. 
Such a host plant may be entered when a mere seedling, in 
which case the fungus grows with its growth, or it may not 
be attacked until older or even mature. The host may be 
permeated in all its parts by the fungus filaments ; or certain 
members, only, such as the leaves, flower parts or twigs, 




Fig. 51.— Young hyphae of Exobasidium developing from spores, .?/, entering the 
air-pores of the leaf of the cranberry. Others, from .</', j/", penetrate the skin 
directly. Magnified about 600 diam — After Woronin, 

may be affected. The effect of the fungus upon the host is 
often scarcely visible to the unaided eye; sometimes a 
local disturbance is manifested by swelling, unnatural color 
or growth;* sometimes the affected members become dis- 
torted and useless or are even killed ; sometimes the disease 
is general and is followed, slowly or quickly, by general 
death of the host. 

52. Infection. — These internal parasites obtain entrance 

* Sec further ""' 222, 464. 



44 



PLANT LIFE. 



to their hosts in various ways. Sometimes the young hypha, 
growing from a special reproductive body (spore),* so minute 
that it may easily float in the air and fall upon a leaf, creeps 
along the surface till it finds one of the 
microscopic openings in the skin of the 
leaf, into which it grows (sp, fig. 51). 
These external openings are connected 
with irregular spaces between most of 
the cells of the softer parts, which are 
also the parts in which the food-supply 
s most abundant. In these, therefore, 
the fungus develops, breaking out to 
the surface again to form or set free its 
reproductive bodies. 

Or, the young hyphae may excrete 
at their tips a substance which so soft- 
ens or dissolves the cell-walls of the 
host that they penetrate these cells 
readily, not only at the surface (sp' , 
sp" , fig. 51), but in the interior. f They 
then branch freely, often growing in 
the spaces between the cells, often 
passing through the cells themselves 

Fig. 52— Hyphae of Fra- l h ° 

metes Pitii perforating the ({\^t C2). 
walls of a wood-cell (at c) ol v °' 3 /' 

Scotch pine and destroying Plants are often attacked when mere 

the primary wall ol the cell. 

d .'.holes made by hypha. seedlings. Either from a bit of my- 

Magnified about 800 diam. ° ' 

—After r. Hanig. celium or a spore which has survived 

the winter or the dry season, a hypha grows, which, almost 
as soon as the seedling emerges from the seed, penetrates it. 
The fungus, in these cases, may develop quickly and kill the 




* See II 304 and the following. 

f It is not improbable that the penetration of cell-walls is assisted by 
such pressure as the growing hypha can exert, hut the relative action of 
enzymes and pressure has not been determined. 



THE FUNGUS BODY OF HYPHAL ELEMENTS. 45 

young plant (as in the "damping off" disease in green- 
houses), or it may develop slowly and not reach maturity 
until the host is mature. 

53. Haustoria. — Those fungi which grow upon the sur- 
faces of living plants (and those which grow in the internal 
air-spaces) often have special branches for fastening them- 
selves to the host or absorbing food from it. In the surface 




Fig. 53. — Epidermis and a few cortical cells of cowberry with mycelium of Calyp- 
tos/>ora occupying the intercellular spaces and pressing knob-like ends against the 
cells from which a slender branch penetrates the wall and enlarges i 



into sac-like haustoria, b, b. a, club-shaped hyphae which produce spore-mother- 
cells, c\ in the epidermis. Magnified 420 diam.— After K. Hartig. 

fungi these are usually very short, disk-like or lobed 
branches which do not penetrate the cells of the host. In 
other cases they are branches of minute diameter, which 
enter the cells, and either enlarge into a knob (fig. 53) or 
branch profusely (fig. 54). 

54. Fusion. — When the hyphre of a fungus grow very 
close together, they frequently cohere and become so 
changed in appearance as to lose all trace of resemblance to 
filaments. Not only fusion but thickening and division 



4 6 



PLANT LIFE. 



occur, and a section of the resulting structure has much the 
appearance of a section of the tissues of ;i higher plant (fig. 
55). These changes arc particularly apt to occur among the 
superficial parts of the more massive structures among the 
fungi, where they are necessary to impart firmness, rigidity, 
or durability. For example : in the ergot, a fungus common 
upon certain grasses, a portion of the mycelium is to survive 
the winter and grow again the next season. This portion 





Fig. 54. Fig. 5-.. 

Fig. 54. — Branching haustoria of Peronospora. m, m, the hypha traversing an 
intercellular space of the host; g, z, two haustoria penetrating two tills of 
the host and branching therein. The other contents of host-cells not shown. 
Magnified about 400 diam. — After De Bary. 

Fig. 55. — A section through the mycelium of a lichen showing hypha; near upper sur- 
face, a, and lower surface, 6, fused into a false tissue ; only in central region are tin- 
filaments recognizable. The dark spheres are imprisoned alga;. Magnified 650 diam. 
— After Bornet. 

replaces the young ovulary of the flower (see 1" 335), and, 
as it matures, becomes a dark-colored mass, as firm and re- 
sistant as the grain itself (fig. 56). 

The interweaving and fusion of the hypha? sometimes pro- 
duce cord-like or strap-like structures of considerable size.. 
The mycelia of the higher fungi frequently form them, and 



THE FUNGUS BODY OF HYPHAL ELEMENTS. A7 



they may be found in the leaf-mold of forests or in rotten 
stumps or between boards in wet places. 




Fig. 56.— a, compact mycelium of ergot in the form of a grain-like body, replacing 
grain of rye ; l>, the same germinating to form reproductive bodies. Natural size.— 
After Tulasne. 

54a. Lichens. — The body of lichens is a mycelium woven 
about isolated unicellular algae, colonies, or filaments, 



48 PLANT LIFE. 

which are thus imprisoned.* The fungus hyphae usually pre- 
dominate and in great measure determine the form of the 
body and its texture. Sometimes the algae are present in 
such numbers that the hyphae seem merely distributed among 
them. In form the body may be broad and thin (fig. 225), 
or slender and shrub-like. In texture it may be tough and 
leathery, with the hyphae near the surface fused into a false 
tissue (a, b, fig. 55). When gelatinous algae, such as Nostoc 
(see •' 13) are imprisoned, the body may be gelatinous. 
In all cases the algae supply the fungus with food, and are in 
turn supplied with water absorbed by the spongy mycelium. 
(See further \\ 195, 223, 462.) 

* Rarely about other small green plants. 



CHAPTER V. 

LIVERWORTS AND MOSSES. 

55. Alternation of generations. — In the liverworts and 
mosses, as in all the plants higher in the scale, there occur 
two well-marked phases in the course of their lives. One of 
these phases is marked by the formation of sexual reproduc- 
tive cells, or gametes (see *H 369), the egg and sperm, 
whence it is called the sexual phase, or the gametophyte . The 
other is characterized by the formation of non-sexual repro- 
ductive cells, the spores (see "[ 304), whence it is called the 
non-sexual phase, or sporophyte. These two phases alternate 
with each other, the sexual reproductive cells of the game- 
tophyte producing, under suitable conditions, the sporophyte, 
whose non-sexual reproductive cells give rise to the game- 
tophyte. To this regular sequence of the two phases the 
phrase alternation of generations has been applied.* 

In the higher liverworts and mosses both phases have 
nutritive work to do, but in many this is confined to the 
gametophyte, and in all the gametophyte carries on the 
greater part of it. To this phase, therefore, attention is 
first given. 

Liverworts. 

56. The thallus. — The form and structure of the vegeta- 
tive body of the simplest liverworts is scarcely different from 

* Rather obscure suggestions of the alternation of generations are to be 
found among the alg;e and fungi, tint they are not definite enough to 
warrant discussion in this book. Let the student notice, however, that 
this feature does not appear suddenly in plant life, though introduced 
abruptly into the account of it. 

49 



50 



PLANT LIFE. 



that of some of the green algae. The body is a thallus with 
rhizoids (fig. 57). The rhizoids are usually linear aggregates 




Fig. 57. — A, plants of Riccia sorocarpa, on the ground. Gametophyte phase. Nat- 
ural size. B, a vertical section of one of the thick lobes of the thallus, showing 
nearly uniform structure. The thallus has nearly covered over two young sporo- 
phytes which appear as though in the interior. Rhizoids arise from the ventral side 
and flanks. Magnified about 25 diam. — After I5ischoff. 



of cells having thin walls and little protoplasm, arising from 
the under side and flanks of the thallus. They serve to 




Fig 58.— Portion of a vertical section of the thallus of Lunularia cruciata. a, 
dorsal, i, ventral epidermis; c, an air-pore; <•, air-chamber, from whose floor rise 
cell-rilainrnis, ,/ ; _/, partition between adjoining air-chambers; g; colorless cells 
containing starch, some showing net-like thickenings of the walls, others with oil- 
bodies, //; 1, a ventral scale ; /, a rhizoid. Magnified 110 diam. — After Nestler. 



fasten the thallus to the substratum, — an adaptation to the 
terrestrial mode of life. The thallus is usually fiat and 



LIVERWORTS AND MOSSES. 



expanded in a horizontal plane, though sometimes much 
crisped. The simpler ones consist of several layers of uniform 
cells* (£, fig. 57). 

57. The dorsiventral thallus. — In other forms there is a 
more decided difference between the upper and under sides 
of the thallus. The upper cells contain chloroplasts, 
while the under ones have none or very few. In the Mar- 
chantia family there are large air-chambers in the upper part 
of the thallus, from the floor of which arise filaments or 
cactus-like rows of chlorophyll-bearing cells (fig. 58). On 
the under side, also, are frequently found scale-like out- 
growths (superficial aggregates), as in fig. 58, i. 

A part which shows constant 
differences between an upper (dor- 
sal) and an under (ventral) side is 
said to be dorsiventral, and the 
state of being thus different is 
termed dorsiventrality. 

58. Branching. — The branching 
of the thallus is always by forking, 
in a single plane or direction, as in 
Fucus, but the branches do not 
always develop equally. Some- 
times special branches, instead of 
remaining horizontal, grow upright 
and develop into peculiar forms 
adapted to producing the sexual 
reproductive organs (fig. 59). 

59. The growing point of the thallus is usually in a notch 
at the apex (fig. 60). There is a single apical cell of wedge 
shape (rarely tetrahedral), from whose inner faces segments 
are cut off (fig. 61). These, by division and growth, 




oung, one mature), f< >r 
g sex-organs. Nal ui tl 
\ti,r Bischoff. 



*Ccenocytes rarely appear in the vegetative bodies of this or any 
higher group. 



52 



PLANT LIFE. 



produce the whole thallus. The center of the thallus is 
generally thicker than the wings, and forms a sort of central 
rib (B, fig. 60). 

60. The shoot. — In the greater number of liverworts the 
mature vegetative body is a shoot, which is differentiated 




Fig. 60. 



Fig. 61. 



Fig. 60.— Surface view of growing apex of thallus of Metzgeria furcata just after 
forking, a, primary apical cell; />, secondary apical cell of branch; c, the wing- 
tissue between axis and branch outgrowing the apices. B, the midrib. Magnified 
160 diam.— After Kny. 

Fig. 61. — Diagram showing origin of branch in Metzgeria furcata. a, primary 
apical cell from which the segments right and left bounded by heavy lines have 
been cutoff. All have undergone further division. In the right-hand one the latest 
cell-walls have been so placed as to form a wedge-shaped cell, />, which becomes 
the apical cell of a branch. Its early formation gives the (false) appearance of 
dichotomy. — After Kny. 



into stem and leaves (figs. 62, 63). Even in such a body 
the dorsiventral character is well marked. The stem is a 
filiform axis of uniform cells, bearing three (rarely more or 
fewer) rows of leaves, of which the two dorsal rows 
are the larger, while the under leaves are much smaller, even 
to being inconspicuous or wanting. These leaves are super- 
ficial aggregates, consisting of uniform cells richly supplied 
with chloroplasts, as are also the outer cells of the stem. 
Their form is very varied and often of great beauty. They 
are always sessile and are usually crowded so closely as to 
overlap each other more or less, and hide the axis com- 
pletely (fig. 63). 



LIVERWORTS AND MOSSES. 



53 



61. The origin of the leaves will be apparent upon com- 
paring figures 64, 65, and 66. In Blasia (fig. 64) the thallus 
is lobed, i.e., the edge has not grown equally, but continued 
growing longer at certain 
points. In Fossombronia ( fig. 
65) the flattened thalloid 
form is still evident, but the 
lobing has become so deep 



€> 





Fig 62. 



Fig. 63. 



Fig. 62.— Gametophyte of Hazztniiti XoTce-Hollandite. Besides the ordinary- 
branches there are slender ones (flagella) with sparse minute leaves. Naturalsize. 
— After Lindenberg and Gottsche. 

Fig. 63.— A, dorsal view; A', ventral view of a piece of fig. 6a, magnified about 12 
diam., showing the stem, bearing two dorsal rows of large leaves and one ventral 
row of small ones.— After I.indenberg and Gottsche. 

that the almost separate parts are usually called leaves. 
In Noteroclada (fig. 66) the central axis is still more com- 
pact, and has lost its flat form, becoming a rounded stem 
from whose flanks arise regular outgrowths, the leaves, each 
of which corresponds to one of the lobes of the thallus in the 
other forms. 

Mosses. 

In the mosses the complexity of the mature vegetative body 
is somewhat greater. It is always developed as a shoot differ- 
entiated into stem and leaves. 

62. Rhizoids. — The shoot is anchored, as in the liver- 



54 



PLANT LIFE. 




Fig. 64 



Fig. 64.— Part of a plant of Blasia pusilla. The flattened lobed thallus is the 

gametophyte; the stalked capsules (one young:, one bursted) are two sporophytes 

attached to it. Magnified 4 diam. — Alter Schiffner. 
Fig. 65. — Gametophyte and sporophyte of Fossombronia cristata. The thallus is 

so deeply lobed thai the divisions are usually called leaves. Magnified 15 diam.— 

After Schiffner. 




Fig. 66.— A, a gametophyte of Noteroclada, with a sporophyte attached. Natural 
size. B, a part of the stem and a single leaf of the same, magnified about 10 diam. 
— After Hooker. 



LIVERWORTS AND MOSSES. 



55 



worts, by numerous usually much branched rhizoids (A, fig. 
67; iv, fig. 68). Similar filaments may be produced, often 
in great numbers, along the stem and especially in the axils 
of the leaves, or they may even arise from the leaves them- 
selves, when the plants grow in dense patches or in a very 
moist place. 




Fig. 67.—.-/, gametophyte of Polytrickum commune, with rhizoids below. /?, 
gametophyte of Hylocomium splendens, bearing three sporophytes near top. 
Natural size. — After Kerner. 

63. The stem is usually cylindrical and covered by the 
crowded leaves. In structure it generally shows an advance 
upon that of the liverworts in having the whole of the outer 
region occupied by a distinct mass of mechanical tissue com- 
posed of thick-walled cells, and, near the (enter, a strand of 
elongated small cells, known as "conducting tissue" (fig. 
68), though it is doubtful whether it conducts anything. 



56 



PLANT LIFE. 




Fig. 68. — Transverse section of the stem of Bryum roseum. In the center the 
small cells make a central strand, the "conducting tissue "; the surface cells form 
an epidermis; the next three rows within also have thick walls an. 1 strengthen the 
stem; w, rhizoids arising from epidermis. Magnified 50 diam. — After Sachs. 





Fig. 69. 

Fig. 69.— A, leaf of a moss [Funaria Americana), showing central rib. Magnified 
about 40 diam.; />', upper portion of the same leaf, highly magnified, showing 
single layer of cells forming the blade and the narrower cells of the thick rib.— 
After Sullivant. 

Fig. 70 —Tip of leaf of a moss (Oligotrickum aligerum\ showing the thickened 
rib, and the plate like ridges on blade and rib greatly increasing the surface of 
nutritive tissue. Magnified about 75 diam. — After Sullivant. 



L 1 1 ~ER IVOR TS A iVD MOSSES. 



57 



64. The leaves arc also more highly developed than in 
liverworts. They are always sessiie and are arranged in two 
(rarely), three, or more vertical ranks along the stem, and 
consist usually of a single sheet of chlorophyll-bearing cells, 
the blade (figs. 69, 70), and a central rib running from base 
to apex (frequently wanting), which is composed of elongated 
conducting and strengthening cells (figs. 69, 70). In some 
the amount of green tissue is increased by the formation of 
vertical plates similar to the blade (fig. 70). 

65. Branching.— The stem branches, often very profusely, 
by the formation of lateral growing 
points beneath the developing leaves. 
Sometimes the growth of the lateral 
branches, as of the original main 
axis, is checked by the formation 
of sexual organs. In that case a 
new branch is likely to arise some 
distance below the apex, so that the 
stem is a succession of lateral 
branches, called a sympodium (fig. 
71). This mode of branching is 
termed sympodial. In other cases 
the main axis continues its growth 
unchecked, and more or fewer 
branches also develop. These lie 
plainly upon the sides of a central 
axis. This mode of branching is 
called monopodia!. Often the 
growth of the lateral axes is defi- 
nitely limited and their develop- 
ment regular, forming a pinnate 
branch-system. If the secondary 
axes themselves branch, there is 
even tripinnate system, as in figure 67, B. 




Fig. 71. Axis of a moss (Ortho- 
trie It u m) showing sympodial 
branching. .V, 5», .V 3 , • 
ii\ e 1 lusters "I sexual organs, 
produced at apex which check 
the growth "I axis. Beneath 
each a lateral growing point 
develops, produi 

the brances /•'. /•''. 6*. Magni- 
fy d n >li. mi. Alter Bruch & 
Scbimper. 

formed a bi pinnate or 



58 



PLANT LIFE. 



66. Protonema. — In its early stages the vegetative body 
of the hafv liverworts and the mosses is either a flat thallus, 
similar to the mature form of the thallose liverworts, or a 
branching filamentous body, called the protonema, almost 
identical with the form of the filamentous algae. Upon this 
protonema the leafy shoot arises as a lateral bud, which soon 
outstrips it in growth and differentiates leaves. The proto- 
nema may live for some months, but generally perishes after 
having produced a few lealy plants. 

67. Sporophyte. — The non-sexual phase in the liverworts 
and mosses has almost no vegetative functions, and a fuller 





Fig. 72. — A, two capsules of Rryum ; from the right-hand one the lid 1ms fallen, 
showing the teeth. Magnified 5 diam />', four gametophyte shoots of Splachnunt 
ampullaceum, bearing four sporophytes. Natural size. C, a capsule "I one <>f 
the same sporophytes, showing enlarged apophysis, a, below the sporangium, j. 
Magnified 10 diam. />. capsule of Splachnum luteum, with umbrella-like apo- 
physis, a, below sporangium, .v Magnified 2 diam. 

study of its structure is left for Part III. It consists at 
maturity of a yellowish or brown spherical or cylindrical case 
(fig. 72), which is sessile or raised upon a short or long 
stalk and contains (a iew or) hundreds or thousands of 
reproductive cells called spores. The base of this stalk 
constitutes an organ called the "foot," which is embedded 
in the gametophyte (_/", fig. 73). 

68. Nutrition. — The surface of the young sporophyte, 
when large and well developed, as it is in the higher liver- 
worts and mosses, is green. To a limited extent, therefore, 
it is able to make food ; but not sufficient for its needs, 



LIVERWORTS AND MOSSES. 



59 



for these arc great on account of its rapid growth and the 
supply required as reserve for 

each spore. The foot, being in 
close contact with the tissue of 
the gametophyte, acts as an 
absorbing organ, receiving food 
solutions from it. The sporo- 
phyte thus lives, in part at least, 
as a parasite upon the gameto- 
phyte. 

In some mosses there is a ten- 
dency to increase the nutritive 
work of the sporophyte by de- 
veloping at the top of the stalk, 
below the spore-case, a mass of 
green tissue. InBryumfyi, fig. 
72) this gives the capsule a pear- 
shape, while in Splachnum {B, 
C, D, fig. 72) it is so far de- 
veloped as to exceed the spo- 
rangium. In some species it is 
expanded into a miniature um- 
brella which, one can imagine, 
might readily become segmented 
into leaves. 

The intimate attachment of sporophyte to gametophyte 
continues throughout the life of the former. Sometimes the 
gametophyte perishes at the close of the growing season, but 
more commonly it is perennial, growing and branching at the 
anterior end as the older posterior parts die away. 




Fig. 73.— Yonni; sporophyte of Phas- 
i urn cuspidatum. c, columella ; f, 
foot, embedded in gametophyte stem; 
s, seta (cells not shown); s/>s, spo- 
rangium ; s/>, spore-mother-cells. 
Magnified 80 diara.— After Kienitz- 
Ge*rloff. 



CHAPTER VI. 

FERNWORTS AND SEED-PLANTS. 

Fernworts. 

Among the still more complex plants, the ferns and their 
allies, the same "alternation of generations" can be seen. 
The two "generations," or phases, have, however, changed 
much in relative size. Whereas in the liverworts and mosses 
the gametophyte is much the larger and more conspicuous, as 
well as the longer-lived, among fernworts the sexual phase is 
so much smaller that it is seldom seen ; and in some species 
it is almost microscopic. On the other hand, the sporophyte 
is the phase which is usually seen and the only part popularly 
known. 

69. The gametophyte. — The vegetative body of this phase 
of the fernworts in its best developed forms 
is a small, flattened, green body of oblong, 
orbicular, or cordate outline, commonly 
less than half a centimeter in diameter, 
rarely as much as 2 cm. (fig. 74). It is 
strikingly like a thallose liverwort in 
general form, being distinctly dorsiventral 
and having rhizoids on its under side, 

Fig. 74. — Ventral side of . , . 

the gametophyte of a which fasten it in place. ( because of this 

lem.Asplenium. The , , . . . . , . , 

notched end is the an- thallOld form and because it seemed to 
tenor. Rhizoids near , , . . ,, , 

posterior emi. Tin small precede the "real plant — a popular 

circles show position of , . , 

male organs ; the chim- phrase meaning the sporophyte — it was 

ney-like projections near ,, , ,i n- \ i-\ -\ \ .1 

anterior end the female Called A />nt/// t l///l/W .) Only the Central 

diam. After k r. part 01 the gametophyte consists of more 

than one layer of cells. On the under side of this central 

60 




J- /.A. VIVO NTS AND SEED-PLANTS. 



61 



"cushion," as it is called, are produced the sexual organs. 
(See further under Reproduction, Tart III.) 

70. Reduction of gametophyte. — In a few of the fernworts 
the gametophyte is filamentous, or tuberous, and more or less 



N 




Fig. 75. — Sporophyte of a fern, Polypodiu 
stem, hearing seenndary roots and 



ilgare, showing horizontal underground 
■s. Natural size. — From Bessey. 



completely subterranean and colorless. Such prothallia derive 
tluir food from decaying plant-offal. 

In higher plants of this group the gametophyte becomes 
still further reduced in size and structurally simplified, until 
in some species it is hardly more than a few cells surrounding 
the sexual organs. These reduced forms grow by the use of 



62 



PLAN T LIFE. 



food stored in the spore from which they originate. The 
gametophyte of such species has lost wholly its vegetative 
character, and is restricted in function to the production of 
the sexual organs. 

71. The sporophyte. — In contrast with the smallness and 
simplicity of the gametophyte is the relatively large size and 




Fig. 76.— Embryo of Pteris aguilina, and a small part of the gametophyte, g y in 
which its foot,/, is embedded, r, the primary root ; s. primary stem ; /, primary 
leaf. Induced growth of the gametophyte about the foot is shown by small size and 
numbei of cells. Much magnified. — After Hofmeister. 







Fig. 77 — Section through embryo and gametophyte of maidenhaii fern (AdiantutH 
Capillus-Veneris). The embryo is older than that in tig. 76. /,/, gametophyte; 
A, rhizoids, among which are two spermaries. The eggs in three ovaries failed to 
develop ; the other formed the embryo, E. a, primary stem, only slightly de- 
veloped (compare s, fig. 76) ; b, primary leaf ; iu, primary mot. The part embedded 
in the fjametophyte is the foot. Magnified about 10 diam. After Sachs. 

complexity of the sporophyte (fig. 75). It is always differ- 
entiated into stem and leaves, and, with rare exceptions, 
roots also. This great advance in the development of the 
sporophyte of the fernworts, as contrasted with its form in 
their nearest of kin below, the liverworts and mosses, suggests 
that the fernworts are a very old group ; a hint which is con- 
firmed by the antiquity of their fossil remains. It is also 
noteworthy that, as compared with mossworts, the chief work 



FEXA'irORTS AND SEED-PLANTS. 



63 



of nutrition has been shifted from the gametophyte to the 
sporophyte j and this even when the gametophyte has its 
largest size and greatest duration, while nutritive work is 
wholly abandoned in the smaller forms. The sporophyte has 
also become the long-lived stage, the gametophyte being 
usually transitory (only exceptionally living more than one 
season), while the sporophyte lives through one season in the 
few annuals, and commonly for several or even many years. 

72. The embryo. — The fertilized egg, from which the 
sporophyte arises, develops while still embedded in the 
gametophyte in which it is formed. Consequently the 
embryo sporophyte is, as in the mossworts, at first surrounded 
by the gametophyte (figs. 76, 
77). The part of the gamet- 
ophyte adjacent to the embryo 
grows under the stimulus of its 
presence, but the growth of the 
embryo is more rapid, and it 
consequently spreads apart the 
gametophyte (see figs. 76, 77). 
A portion of the embryo de- 
velops a temporary organ, the 
foot, which remains embedded 
in the gametophyte until the 
first root, stem, and leaf have 
been formed (fig. 78). Soon 
thereafter the gametophyte per- 
ishes and the foot, no longer 
useful, disappears. 

73. Members. — The mature 
sporophyte is differentiated into 
root, stem, and leaves. The 
important adaptations of the 
structure and-forms of these members are so similar to those 




Fig. 78 



same as fiff. 77 



The gametophyte, /\ seen from be- 
low, w 11 li 1 In.-. lids ; the sporophyte 
•-nil attached Inn with primal \ leaf", .'. 
developed into blade and stalk ; /. the 
primary root: .-. .1 secondary runt, 
arising from tin- juncture oi 
and st<-iii Magnified about 4 diam. 
After Sachs. 



64 PLANT LIFE. 

of the seed-plants that thay will be discussed in connection 
with them. 

Seed-plants. 

Among the highest plants, those which produce seeds, the 
differentiation of the body is essentially the same. The 
alternation of sexual and non-sexual phases is still traceable, 
though greatly obscured by the extreme reduction of the 
gametophyte. This tendency to the reduction of the sexual 
phase, which was remarked in passing from the mossworts to 
the fernworts, continues, until in the highest seed-plants the 
gametophyte is wholly microscopic. Even by the aid of the 
microscope, it is possible to identify only the sexual organs 
which it produces, and one or more cells which are, perhaps, 
the rudiments of its vegetative body. The sporophyte, con- 
sequently, is the only phase of the seed-plant visible to the 
unaided eye. The relation of the gametophyte to it will be 
explained in Part III. 

The body of the sporophyte exhibits the same members, 
viz., stem, root, and leaf, having the same general form, and 
subject to the same modifications, as in the fernworts. To a 
discussion of the vegetative members of the fernworts and 
seed-plants we now turn. 



CHAPTER VII. 

THE ROOT. 

74. Analogous members. — It has been pointed out that, 
among the lower plants, there are very many which possess 
structures similar in form and function to the root, and 
sometimes called by the same name. Although these parts 
serve to hold the plant in place, and perhaps to absorb 
material from the substratum, they are not to be looked upon 
as homologous with the roots of the higher plants, but as 
merely analogous with them. In the plants whose vegetative 
body is a thallus the gametophyte is the prominent phase. 
In no case does the gametophyte produce true roots. It is 
not until the sporophyte becomes an independent plant that 
true roots are found in the vegetable kingdom. It is, there- 
fore, only among fernworts and seed-plants that these organs 
are to be found. When the sporophyte is developed as an 
independent plant, it becomes necessary for it to produce 
some organ capable of holding it in place, or of absorbing 
materials from the outside, or of doing both. The organ 
developed to meet this need is the root. 

75. Primary roots — In accordance with their origin, 
roots are either primary or secondary. Primary roots are 
those which are developed directly from the egg from which 
the entire plant takes its rise. The spherical egg in most 
of the fernworts begins its development by a division into 
hemispheres. The hemispheres divide into quadrants ; ea< h 
of the quadrant cells divides into two, forming octants of the 
original egg. Division continues and the fundaments of 
primary root, foot, stem, and one or more leaves appear 

65 



66 



PLANT LIFE. 



(see fig. 76). In many of the seed-plants the egg divides 
several times in parallel planes, forming a 
short filament, the suspensor (figs. 79-82). 
The terminal cell of this row may then 
give rise to an embryo, as just described, 
or this terminal cell and an adjacent one 
may take part in forming the embryo. In 
this case the terminal cell, by its divisions, 
either produces the primary leaf or leaves, 
t produces the primary stem and 
r, s, ceils of the suspen- leaves ; while the second cell gives rise to 

sor; a, a, fi, cells from ° 

:1V H.Khiy r ^: the P rimar y stem and root > or to the 

fied. -Afur Sachs. primary root alone (see figs. 80-82). 
The two primary members formed 
from the root hemisphere of fernworts 
are not always permanent. The foot is 




Fig. 79.— A very young or 

embryo of the onion. 






Fig. 80. Fig. 81. Fig. 82. 

Fig. 80.— A very young embryo of shepherd's-purse. Suspensor, s, s. just completed, 

and first four cells of embryo formed by division of terminal one ; the sei ond 1 ell, 

/>, is to produce part oi the root. Highly magnified. — After Hanstein 
Fig. 81. — An older stage of the same. /.', embryo; /•', /■". two cells resulting from 

division of b. fig. 80; *. s. suspensor. The shaded cells produce the skin and the 

vascular bundles Highly magnified.— After Hanstein. 
Fig. 82.— An older embryo of same. £, embryo; /. /, primary leaves; .9/. apex of 

stem ; r, primary root ; re, first layer of root-cap; .r, suspensor. Cells shown only 

in part. Less magnified than preceding.- \fter Hanstein. 



THE ROOT. 67 

always temporary, disappearing as the embryo becomes 
larger. It is sometimes wanting from the first. In both 
femworts and seed-plants the primary root is rarely wanting, 
but often short-lived, dying after the plant has established 
itself and has formed secondary roots to take its place. In 
many cases, however, the primary root persists throughout 
the life of the plant. 

76. Secondary roots. — Secondary roots, on the contrary, 
are those which arise upon stem or leaf, or even upon the 
primary root itself. In the last case they are distinguished 
from branches of the primary root, which arise in regular 
succession toward the apex, by originating out of this regular 
order. Secondary roots are also called adventitious roots. 
They may take their origin at any point upon any of the 
members. Their point of origin will depend largely upon 
external conditions. They are especially likely to be formed 
upon those parts which are in contact with the substratum, 
or from those parts which are kept moist. Upon stems they 
are most apt to appear near the nodes. (See 1 119.) If 
the plant as a whole is surrounded by very moist air, roots 
may appear at any point of the surface. Secondary roots 
arising thus upon a part of the plant exposed to the air, and 
growing for all or part of their existence in the air, are also 
called aerial roots. Familiar examples are to be seen about 
the lower part of the stem of Indian corn, the English ivy, 
the poison-oak, the trunks of palms and tree-ferns. Secon- 
dary roots often arise in regular succession toward the grow- 
ing apex of the stem, particularly in plants which have creep- 
ing or subterranean stems. 

77. Growing point. — Primary and secondary roots do 
not differ materially in their structure. The early divisions 
of the quadrant cell which produces the primary root in tern- 
worts are so arranged that a cell shaped like a four-sided 
pyramid is produced. This cell becomes the apical, or 



68 



rLANT LIFE. 



initial, cell. It is situated with one face directed toward the 
apex of the root (see fig. 83), and the other three faces 
within it. Parallel to the three inner faces partitions are 
constantly formed in regular succession dividing this apical 
cell into two unequal portions, so that the smaller is looked 
upon as a segment cut off from the larger portion. If these 
inner faces be numbered respectively 1, 2, 3, the segments 
are constantly produced in the 
order of the numbers. These 
segments themselves divide to 
form other cells, and thus give 
rise to all the tissues of the root. 
This mass of actively dividing 
cells is the primary meristem or 
growing point of the root (com- 
pare • 101). As the older cells 
of the primary meristem enlarge, 
divide, and differentiate, they 
are constantly pushing the apical 
cell further away from the older 
part. Not only' are segments 
cut from the three inner faces of 
the apical cell, but, at less fre- 
through the extremity of a root of quen t intervals, partitions paral- 

Marsiha. 1 he larjic triangular cell 1 » ' I 

near center of figure is the apical le | t0 tne outer f ace f Qrm s j m j_ 

cell. I lie segments from the inner 

faces may be readily traced back- p u se gments. The division of 

ward; thus the dotted line e< points ° 

to the fourths to the sixth segment tnese sc <r ment S oiveS HSe tO 3. 
from the posterior n.nht-hand tare "1 ° ° 

apicaiceii. e/>, root -ca P (epiderm.s); s t rU cture covering the very tip 

ec. cortex; c, stele; en, endodermis o • 1 

(pan .,f cortex^; fie , peri. v. i. (part f the root, and connected with 

of stele). Magnified about ioo diam. 
After Van Tieghem. it for a short distance only. It 

receives, therefore, the appropriate name of root-cap {ep, fig. 

83). Since the cells of the surface of the root-cap are older 

and firmer than the inner segments and the initial cell, and 

lie in front of them, they serve to protect the more delicate 




Fig. 83.— Medial, longitudinal section 



THE ROOT. 



69 



cells as the growth of those behind constantly pushes the 
apex forward through the soil. 

In seed-plants, the segments of the egg which produce the 




^v 



Fig. 84. Transverse section of a young root (frown in soil, showing root-hairs with 
adherent soil-partii les, the cortex, and the stele. Magnified about 20 diam.— After 
Frank. 

root do not divide so as to form a single apical cell, but a 
group of initial cells, which retain tin- power of rapid division 
and constitute a primary meristem or growing point. In all 
other respects the development of the root from this group 
of initials is similar to that already described. 



7° 



PLANT LIFE. 




In both cases, the differentiation of cells produced at the 
growing point results in the formation of three characteristic 
parts of the root, namely, (i) an outer layer or layers, the 
epidermis ; (2) an inner region, the stele ; (3) between these, 
the cortex. 

78. 1. The epidermis usually becomes many-layered. 
At the apex it constitutes the root-cap (ep, fig. 83). On the 
other parts of the root it sometimes sloughs 
off entirely, exposing the cells of the cortex 
itself, as in the monocotyledons (lilies, 
grasses, sedges, etc.); or, more commonly, 
only the outer layer sloughs off, leaving the 
innermost as the covering of the cortex. 

79. (a) Root-hairs. — Those cells which 
form the surface of the root, 
whether they be the origina 
epidermis or cortical ones 
which have been exposed 
by its loss, usually develop 
a large number of hairs, 
known as root-hairs (fig. 
84). These root-hairs are 
branches of the superficial 
cells ( fig. 85), and maybe 
looked upon as simple ex- 
tensions of them, as the 
finger of a glove is the 
extension of its palm. Only 
one root-hair arises from a 
superficial cell. They arc 
usually unbranched and without transverse partitions. Only 
in rare cases are they wanting. They live for a shorter 
or longer time, but are always, as compared with the 
duration of the root, quite transient. The older part of the 




Kig. 85. — Two root-hairs showing structure 
and relation to superficial cells of root; 
grown in water and therefore not distorted 
as in fiji. 84. A, the younger ; />', older, 
nearly mature. n, nucleus embedded in 
cytoplasm; vacuole single and very large. 
Highly magnified.— After Frank. 



THE ROOT. 71 

root, therefore, is without root-hairs because of their death. 
The youngest part of the root is likewise free from them, 
because they have not yet been produced. As the root grows 
in length, new root-hairs are continually being produced and 
the older ones are dying at an equal rate, so that a zone 
of hairs is found only upon the younger parts of the roots. 

80. (/>) The root-cap, serving to protect the tenderer por- 
tion of the root behind, is itself constantly exposed to injury. 
The outer and older cells of the root-cap are, therefore, either 
torn away through mechanical contact, having become gradu- 
ally loosened from each other with age; or, losing their 
active contents, they degenerate and break down into a 
slightly mucilaginous material which facilitates the passage of 
the root through the substratum. This degeneration or the 
mechanical wear is repaired constantly by the formation of 
new cells in the growing point. The thickness of the root- 
cap, therefore, is maintained throughout its existence without 
considerable change. It rarely becomes more than a few cell- 
layers thick. Since its tissue is produced only by the division 
of the apical cell or cells, it is organically connected with the 
root only at the very tip; but it usually extends backward over 
the root, by reason of its growth, for a considerable distance. 
If the finger be supposed to represent the root, a short finger- 
stall, if it were attached to the tip of the finger, might be 
fairly taken to represent the position of the root-cap. Only 
in rare cases is the root -cap entirely wanting. 

81. 2. The stele. — Occupying the center of the root, and 
surrounded on all sides by the cortex, is an aggregate of 
tissues called the central cylinder, or stele (figs. 84, 86, 89). 
The outermost layer of its cells is the peru vele (figs. 86, 88, 
89). Within this are found strands of elongated cells or 
cell-fusions,* called vascular bundles, or strands. These 

* These are continuous chambers formed by the breaking down of the 
partition walls between the abutting ends of cells. They are usually 
devoid of living contents. 



7 2 



PLANT LIFE. 



bundles are of two kinds, xylem bundles and phloem bundles, 
so placed that they alternate with each other about the 
periphery of the stele (figs. 86, 88, 89). The xylem bundles 
may be in contact with one another in the center, or the 
center of the stele may be occupied by a pith (figs. 86, 89). 




Fig. 86. — Transverse section of the stele and a portion of the surrounding cortex of the 
root of calamus, j, .v, innermost layer of cortex, the endodermis, adjoining outermost 
layer of stele, the pericycle; /. xylem bundles; ph, phloem bundles. The shaded ele- 
ments of xylem bundles are the primary xylem ; the large ones, g, are secondary. In 
the center of the stele and between the bundles is conjunctive tissue. Highly magnified. 
— After Sa< lis. 

The tissues of the xylem are usually lignified (see ^[ 9) 
and, when abundant, make up what is called the wood. They 
are the chief water-conducting elements of the older parts of 
the root. 

The tissues of the phloem are usually not lignified, and the 
most important ones are the sieve-lubes, which conduct proteids 
from above to the growing regions of the root. 



THE ROOT. 73 

The number of vascular strands constituting the stele is 
various, being as few as four or as many as forty. The 
ordinary number, however, is from eight to twenty. (See 
figs. 86, 89.) 

82. 3. The cortex generally consists of large thin-walled 
cells which have become partially separated from each other, 
leaving larger or smaller intercellular spaces (figs. 86, 89). 
Its innermost layer, bordering the stele, is usually quite 
different from the rest, and is recognizable by its wavy, radial 
walls, which are suberized (^[ 9). This layer is called the 
endodermis (figs. 86, 88, 89). 

83. Duration. — Even when the primary root persists 
throughout the entire life of the plant secondary roots often 
appear. When the primary root perishes, its functions must 
be performed wholly by secondary roots, which are developed 
in succession upon those parts where they are useful. The 
secondary roots themselves may be either permanent or tran- 
sient. In creeping plants particularly, whether growing on 
land or in water, the functions of the root are likely to be 
handed on to successively younger roots, the old ones perish- 
ing and dropping off. If the roots endure for a considerable 
time, they may retain their primitive structure and form, or 
they may undergo secondary changes which unfit them for 
absorbing organs, and adapt them to subserve various special 
functions. 

84. Secondary changes. — Shortly after any portion of the 
root has ceased to increase in length, and, therefore, within 
the first season, it ordinarily undergoes minor secondary 
changes which may or may not be followed by more profound 
alterations. These changes affect its primary structure in 
various ways and to various degrees according to the parts 
concerned. 

85. 1. External secondary changes. — In some cases the 
older roots differ from the younger in scan civ more than the 



74 



PLANT LIFE. 



loss of the external layer of cells, from which the root- 
hairs arose. The sloughing off of this layer of cells carries 
with it the hairs themselves and exposes the next inner layer 
of cells, which had before become slightly altered so as to be 
rather impervious to water. Upon their exposure, this altera- 
tion proceeds further, so that they become almost or quite 
incapable of being penetrated by the soil-water to which they 
may be exposed. It follows from this that it is only the 
younger part of the root, that is, the portion which has not 
undergone secondary changes, which is capable of absorbing 
water. In many roots this is the only change which occurs. 
In a greater number certain tissues become thick-walled, so 
that the root is also strengthened. 

In a few instances, the root-cap is cast off from the tip. 
This, however, only occurs when the growth in length of the 
root is permanently stopped. 

86. 2. Internal secondary changes. — In a large number 
of roots, especially those 
\ 'of dicotyledons and gym- 
'1 nosperms, the secondary 
changes result in increasing 
the diameter, sometimes 
very greatly. Increase in 
diameter comes about by 
the formation of concentric 
layers of new tissue in two 
or more regions. The new 



J©" 



o 



Fig. 87. — Transverse section of the periphery of , 11 , _j„__j ■ u 

the root ol Clusia, showing the formation of Cells aie piodliced 111 each 

periderm, ec, cells of cortex: ap, the super- .:_._ l . 1, »: 

ncial cells of the root (suberized); per, the region by tile resumption 

periderm, its inner cells (opposite per) actively ,- ,• 1 • , • 1 

&yidmgbytangentialwalls,itstw,M,ute.l.v.rs. ot active division 111 a layer 

//'.snheri/.id. its innermost layer,///, the phello- r 11 1 ■ 1 
derm. Highly magnified.— After Van Tieghe" 

temporarily inactive. 



:ells which had been 
This region is then (ailed the cambium 
or secondary tnerisiem (see^i 77). The divisions which ensue 
in these cells are in the main parallel to the surface of 



THE ROOT. 



75 



the root, that is, they are 
tangential divisions. 

The outer growing layer 
or cork cambium is in the 
great majority of plants 
formed from the cells of the 
pericycle, but it may be 
produced by some of the 
cells of the cortex. In any 
case the tissues which arise 
from this division are of 1 *" 
such a nature as to protect 
the parts within. They con- 
stitute the periderm (fig. 87), 




■Transverse section of two bundles 
from the periphery of the stele of root of broad 
bean (/ 'icia Faba) at the beginning of secon- 
dary thickening. The xylem bundle, g, is 
shaded: the phloem bundle unshaded. ?■, the 
stelar cambium; /, the pericycle. aiso showing 
tangential divisions in parts ; s, the endoder- 
mis. Highly magnified. —After Haberlandt. 




Fig. 89 Transverse section of thesteleol root of bean {Pkaseolus multi/hrus) shortly 
aftei set ondary thii ki ning has b< gun r, endodermis; ,.", . peril yi le; /■. phloem bundles; 
/, primary xylem bundles; <_• . j, ' . se< ondarj xylem; , stelar cambium; M, central pith. 
Compare with fig. go. Highly magnified Attn Sachs. 



7 6 



PLANT LIFE. 



and are ordinarily cork-like, i.e., thin-walled and impervious 

to water. Those cells which lie outside a layer of cork are 

therefore cut off from a supply of food and soon perish. 

The inner growing layer, or stelar cambium, is developed 

within the stele and follows a 

tortuous course, lying outside the 

xylem and inside the phloem 

bundles (fig. 88). As a result 

of tangential divisions in this 

region, tissues similar to those 

already existing in the stele are 

produced. On the outer side 

the cells differentiate mainly 

into the tissues of the phloem, 

and on the inner side mainly 

the older into those of the xylem, often 

^/ f ^S*«Ta1te b r e %VcoX" formin 8 a nearl 5' ^broken mass 




^Hs'of each (figs. 89, 90). The 

lative amount of the different 

tissues which make up these 



ably. Compare with fig. 89, which 
about five times as highly magnified 



b, b, b, b, four primary phioem bundles; 1 eld 
b', secondary phloem produced by 
stelar cambium, as are the four wedges 

b^^^^-iSSSfLSft bundles goes far to determine 
l!^riS-Af^S emwedges) th e character of the mature root. 
87. (a) Woody roots. — If mechanical tissues predominate, 
particularly in the xylem, the root will become strong and 
rigid, as in the case of trees and shrubs. When the root is 
long-lived, the activity of this stelar cambium is usually 
resumed with each season, a layer of tissue being thereby 
added to the outside of the xylem region, and a thinner layer 
to the inside of the phloem. The woody part, especially, 
shows in cross-section concentric rings indicating the yearly 
additions. Since the material produced by the stelar cam- 
bium usually greatly increases the diameter of the root, the 
outside parts become fissured lengthwise. Thus, in an old 
and much-thickened root of the woody type, the periderm 



THE ROOT. 



77 



and the phloem region, with the cortex between them, if 
anything is left of it, constitute a bark, which becomes fur- 
rowed lengthwise, like the bark of the stems of many trees. 
Such secondary thickening finally produces in the roots a 




Fig. 91. — .-/, diagram of primary structure. /•', C, diagrams showing the results of 
secondary thickening from the stelar cambium in the two extreme forms c, cortex ; 
<>.•, endodermis ; />, pericycle ; ph.', primary phloem; //;'', secondary phloem; .1', 
primary xylem ; x", secondary xylem ; cb, stelar cambium; r', secondary pith-rays ; 
in, pith. After Van Tieghem. 

structure which is almost identical with that of stems which 
have undergone secondary thickening. (Compare ^[ 133.) 

88. {!') Fleshy roots. — but if thin-walled cells are the 
predominant products of the stelar cambium, the root often 
becomes very thick and fleshy, as in the carrot, turnip, 
radish, sweet potato, beet, dahlia, artichoke, etc. Such 
roots serve the plant as storehouses of reserve food, and are 
consequently useful to animals as food. The thin-walled 
cells which are produced in such volume may belong to the 
phloem region, as in the carrot and parsnip, or to the xylem, 
as in the radish and turnip. This thickening for storage 
purposes may affect either the primary or secondary roots, 
or both. Other plants may develop the cortex (orchids) or 
the pith (daffodils) to an extraordinary degree, forming 
fleshy roots which also function as storehouses. 

89. (c) Float roots. — In plants which grow in water or 
in very wet swamps, roots are sometimes modified to serve is 
floats. In these cases, the voluminous cortex consists of large 



/8 PLANT LIFE. 

cells, with huge intercellular spaces which are filled with air. 
The root thus serves to buoy up the parts of the plant to 
which it is attached. 

90. ((/) Tendrils, thorns, etc. — In a very few plants, 
aerial roots are modified into tendrils, being slender, sensitive 
to contact, clasping the objects which they touch, if of 
suitable size, and thus assisting the plant to climb ; in some 
instances they are altered into thorns, being short, rigid, and 
sharp-pointed ; in others, being exposed to the light, they 
develop chloroplasts, which enables them to act as organs for 
the manufacture of food. 

91. Branching. — Both primary and secondary roots may 
branch. The mode of branching is of two sorts, either by 
dichotomy, or by the production of lateral branches. 

92. {a) Dichotomy occurs only in a few fernworts, whose 
roots possess a single initial cell. In this case, however, 
the single initial cell (^[ 77) is not divided into two equal 
parts by a partition-wall, as in true, dichotomy (see ^| 103), 
but the initial of the new branch arises from a very young 
segment as in Metzgeria (see fig. 61). The result is a fork- 
ing which cannot be distinguished from a true dichotomy. 

93. (b) Monopodial branching. — In the common mode 
of branching, the monopodial, the central axis grows most 
vigorously, and bears lateral branches upon its sides. The 
normal branches arise from lateral growing points, which 
originate in regular succession behind the apical growing 
point. But sometimes branches appear out of this regular 
order. Such are called adventitious roots. (See *[ 76.) 

94. Position. — Whether regular or adventitious, the posi- 
tion of the growing points is determined by the vascular 
bundles in the stele, since they originate opposite the xylem 
bundles, or with definite relation to them. (See figs. 92, 
93.) The number of vertical ranks of branches can, there- 
fore, be predicted with some certainty from the structure of 



THE ROOT. 



79 



the root. While the angular diver- 
gence is thus quite regular, the longi- 
tudinal intervals at which the branches 
will be formed, which determines 
their distribution along the length of 
the root, are unequal (fig. 92). 

When secondary roots arise from 
the shoot, they have a fixed relation 
to the leaves, or they are formed 
upon the buds produced in the axils 
of the leaves, or they may arise at 
indefinite points along the internodes. 
In the first case, roots may be pro- 
duced either opposite a leaf, or in 
pairs, right and left of the base of the 
leaf. 

95. Origin. — The origin of root- 
branches and of secondary roots is 
rarely exogenous ; that is, the root is 
not commonly produced by the divi- 
sion of cells which lie upon the sur- 
face of a member. In the great 
majority of cases the origin of the 
roots is endogenous ; that is, the for- 
mation of the root is begun by the 
division of cells lying in the interior 
of the member producing it. In most 
cases these divisions begin very near 
to the surface of the stele, either just 
without it, in the endodermis, or just 
within it, in the pericycle. Soon a 
growing point is formed (fig. 93). 




/jr* 8 * -8 " 



X 



The rootlet is thus ii 
completely hidden, 



early stage 



beinj 



buried 



'IG. 92. — Seedling pea. showing 
three \ ei tii a) ranks ol brani li- 
es aloiig the main root. These 

are numbered t, 2, 3. Natural 
size.— After Krank. 



So 



PLANT LIFE. 



beneath the cortex, through which it gradually makes its way 
by the destruction of the tissues ahead of it, partly through 
disorganization of the tissues by pressure, and, probably, 
partly through actual digestion and absorption of the material 
of these cells. When the rootlet reaches the surface it 
emerges, therefore, from a distinct rift in the cortex (fig. 94). 




Fig. 93 



Fig. 93.— Transverse section of a root of a fern (7 '/,•>/.? cretica), passing through the 
axis of a rootlet which has not yet emerged. Only the stele and three rows of cortex 
shown, a, apical cell of rootlet, forming anteriorly the root-cap. <■/>, and posteriorly 
the body of the root, ec, e, c, pd\ b, binary xylem bundles; /, phloem bundle with its 
fellow opposite; /V, pericycle; at, endodermis; /, temporary digestive pouch, in 
course of disorganization and digestion; d, cells of cortex, which will be disorgan- 
ized as rootlet advances. Highly magnified— After Van Tieghem. 

Fig. 94— The same as fig. 93, but older; not quite so much magnified. Tbe'rootlet 
is just emerging from the parent root. /</, c, stele of the rootlet ; ec, its cortex; 
</, disorganized cells of cortex, ec', of parent root; /-', secondary xylem; other letters 
as in fig. 93.— After Van Tieghem. 



96. External conditions. — Branching of the root is often 
profuse, and is dependent very largely for its character upon 
the conditions under which it takes place. In those roots 
which penetrate the soil, it is profoundly modified by the 



THE ROOT. 8 I 

character of the soil itself and the amount of moisture and 
organic matter in it. 

97. Buds. — New shoots may be formed by the roots, either 
as a result of injuries, or normally. In a partially developed 
form, these constitute buds (see ^j 101). Whether formed 
as a result of injuries or normally, they are known as adven- 
titious buds. They arise in the same places and develop in 
the same way as lateral roots ; that is, they are endogenous, 
and, as they continue to grow, burst through the cortex. 
The shoots so produced grow in the normal manner. Very 
rarely the growing point of the root, casting off the root- 
cap, becomes itself the growing point of the shoot. This 
alteration is usually the result of artificial reversal of the posi- 
tion of the root, being brought about in some potted plants 
by turning them upside down. 



CHAPTER VIII. 

THE SHOOT. 

98. The gametophyte shoot. — If plants could be examined 
in the order of their development, it would be discovered 
that the shoot has been evolved earlier than the root. It 
makes its appearance first in the leafy liverworts and in the 
mosses, in which the gametophyte and sporophyte each form 
a stem. The gametophyte differentiates its secondary shoot 
into a stem and leaves. This stem in liverworts is a slender 
cylindrical body of very simple structure, upon whose flanks 
arise leaves which consist of a single layer of cells only. 
(See ^ 60. ) Neither the stem nor the leaves are homologous 
with the stem and leaves of the higher plants. In the stem 
itself one finds all the cells practically alike, so that little 
differentiation of tissues has yet occurred. In mosses, how- 
ever, the gametophyte stem shows some advance, in that its 
tissues are clearly differentiated, the outer being transformed 
into thick-walled cells, in order to give mechanical rigidity 
to the stem, while the innermost, remaining slender, are 
much elongated and serve the purpose, it may be, of con- 
duction. (See ^[ 63.) This differentiation is naturally more 
marked in those mosses which are erect and whose body 
becomes largest, since in these the need for rigidity and con- 
duction of food materials from one part to the other becomes 
greater. In both groups the branching of the gametophyte 
shoot is like that of the sporophyte shoot of some of the 
higher plants, except that the branches never stand in the 
same relation to the leaves. (See •' 65.) 

82 



THE SHOOT. 83 

99. The sporophyte shoot. — The shoot developed by the 
sporophyte of mosses and liverworts forms no leaves, but 
develops as a slender cylindrical stalk, at the distal end of 
which the capsule containing the spores is formed (figs. 64, 
73). It is rather difficult to see in this cylindrical stalk the 
homologue of the leafy stem developed by the sporophyte of 
the fernworts ana other plants. 

The simultaneous performance of the work of nutrition and 
of sexual reproduction proved impracticable, as shown by the 
development of the liverworts and mosses, which are all 
humble plants. The fernworts, originating probably at an 
early period from the same ancestors as the liverworts, sep- 
arated the two functions and laid the chief work of nutrition 
upon the sporophyte. The advantage thus gained enabled 
the extinct fernworts to develop into plants of tree-like size, 
and to become the ancestors of all the seed plants. 

The gametophyte shoot was, comparatively, a failure ; the 
sporophyte shoot was a marked success. It has become 
adaptable to many conditions and many functions. To 
accomplish this its members have been extensively modified 
in form and structure in various plants. The development 
and mode of branching, together with the various forms 
which the shoot assumes, are now to be discussed, to be fol- 
lowed by an account of the two members, stem and leaf, into 
which it is usually differentiated. 

100. Primary shoot. — The shoot which develops from the 
fertilized egg is called the primary shoot. A very few excep- 
tional plants are found in which no primary shoot develops, 
although there are a number of cases in which the primary 
shoot becomes early aborted, and its pla< e taken by secondary 
shoots arising from the root. The primary shoot normally 
arises in fernworts from the anterior half of the egg. The 
anterior hemisphere usually divides into two quadrants, one 
of which develops into the primary leaf, and the other into 



8 4 



PLANT LIFE. 



the primary stem. The stem quadrant, by repeated divisions, 
quickly specializes a central cell, which becomes the apical 
cell of the new shoot. Ordinarily it takes the form of a 
three-sided pyramid, whose base forms the extreme tip of the 
developing shoot (s, fig. 76, /, fig. 95). From the three inner 
faces, as described for the root (^f 77), segments are constantly 
formed, whose further divisions produce all the tissues which 
constitute the members of the mature shoot, i.e., the stem 
and the secondary leaves. In some fern worts and in the seed 
plants, the posterior hemisphere resulting from the first divi- 
sion of the egg grows into a filament called the suspensor, 
and the primary shoot develops from the anterior hemisphere. 
(See fig. 80.) In these plants ordinarily two or more cells 
at the apex of the primary shoot are specialized as the initial 
cells, and from their segmentation arise the tissues of the 
whole shoot, as in the fernworts. 




Fig. 95. — Median longitudinal section through the apex of a shoot of the horsetail 
( Eg ui.u •turn. ,i> vense), showing primary meristem and the form of the growing point. 
t, apical cell, from whi< h a segment, .V, has just been cut off by wall/. S' , a seg- 
ment previously cut off, has divided by wall m. /,/"',/", successively older leaf 
fundaments; g, the initial cell of a branch. Magnified too diam.— After Strasburger. 

101. Primary meristem. — Whether the tip of the shoot 
be occupied by a single initial cell or by a group of initials, 
the apical region, in which the formation of new cells is 



THE SHOOT. 



85 



taking place, is called the primary meristem (fig. 95). This 
primary meristem has no definite limit below, but passes 

insensibly into the permanent tissues. The tip of the shoot 
may be either a sharp cone or a low dome. Between these 
forms a complete series of gradations exists. Below the apex 
the shoot begins to show a differentiation into a central axis 
and lateral outgrowths. The first of these to appear are 
swellings which form the leaves. Later, above the leaf 
fundaments may appear the fundaments of the lateral shoots. 




Fig. 06. — Diagram of a section through a bud / ', the apex; i, 2, 3, 4, successively older 
leaf fundaments; a, 6, c, successively older branch fundaments; </, e, vascular bundles. 
—After Hansen. 

The older leaves upon the sides of the axis outgrow the 
younger ones and the developing axis, and arch over them 
in such a way as to form a more or less compact structure, 
which is a terminal bud. A bud is, then, an undeveloped 
shoot, whose older leaves protect the younger, and particu- 
larly the primary meristem (fig. 96). From the terminal 
bud arise all the members of the primary shoot. 

102. Differences from root. — From what has been said of 
the origin of the shoot, it will be observed that it is dis- 



86 



PLANT Lli-E. 



tinguished from the root by not forming through segmenta- 
tion from the outer faces of the initial cell or cells a many- 
layered epidermal cap. In further contrast with the root, 
which often has no true epidermis except the root-cap, the 
shoot is characterized by possessing an uninterrupted epider- 
mis over its entire surface, consisting always at first of a 
single layer of cells. This epidermis persists as a surface 
covering either throughout the life of the shoot, or for a long 
period, being replaced only upon the 
older surfaces of the axis by subsequently 
formed protective layers. (See • 134-) 
103. Branching. — branches of the 
shoot arise from lateral buds, which are in 
all respects similar to the terminal buds 
just described. If, for any reason, the 
terminal bud of the stem becomes de- 
stroyed, or its growth arrested, a branch, 
developing from a lateral bud near by, 
may assume the position and habit of 
the main axis, its own normal mode of 
development being altered. In many 
plants the death or arrest of the ter- 
minal bud recurs at regular intervals. 
In such plants, therefore, the main axis 
is really a succession of lateral branches, 
and the branching is said to be sympo- 
dial (fig. 97). In some plants, e.g., 
lilac, two lateral buds standing at the 
same level may develop, if the terminal 
one fails. In this case the shoot seems 
to divide into two equal branches. This, 
however, is not true, but false, or sym- 
/>(><Ii\il, dichotomy. True dichotomy, like true dichotomy of 
the root, occurs only in those plants in which the axis has 




I ig 97. Shoot of Euro- 
pean linden, t, the last 
internode formed by the 
liiid of present season. 
This dies and drops off 
and the shoot will be 
formed next year by the 
last axillary bud, a, 
which a] ipi .irs to be 
terminal alter loss of t. 
Half natural size.— After 
Frank. 



THE SHOOT. 87 

a single initial cell. The initial in these cases divides into 
two equal parts, each of which becomes the initial of a new 
branch. Ordinarily, however, the terminal bud develops 
without interruption. In case it is more vigorous than any of 
the lateral buds, the plant will have a central axis, from the sides 
of which distinctly smaller branches arise. If, however, the 
lateral buds are almost or quite as strong as the central one, 
the plant seems to be broken up into branches, and, after it 
has attained its mature form, no one can be pointed out as 
the main axis.* Such branching is monopodia!. These two 
types of monopodial branching and the sympodial type are 
all illustrated in the forms attained by common forest trees. 
(See frontispiece.) 

104. Inflorescence. — Especially profuse branching com- 
monly occurs in the parts of the seed plants where flowers are 
produced. Such clusters of branches bearing flowers constitute 
an inflorescence. Each sort has received a special name which 
not only indicates the type of branching, whether sympodial 
or monopodial, but also the relative length of the branches. 

If the branching is monopodial and each lateral shoot is 
unbranched, the inflorescence is a raceme. If the lateral 
shoots are very short, it is a spike. If the main axis also is 
very short, it is a head. If the main axis is short and the 
lateral axes long, it is an umbel. If the lateral axes are of 
unequal length, so as to bring the flowers to about the same 
level, it is a corymb. If the branching is sympodial, various 
forms of the cyme result. Several combinations of these 
inflorescences are possible. f 

105. Axillary buds.— Lateral buds are ordinarily formed 
in definite relation to the leaves. They stand usually in the 

* The obscurity is greatly increased by the death of more branches than 
survive, owing to various causes resulting in poor nutrition or disease. 

f For further discussion see Gray: "Structural Botany," p. 144; 
Goebel : " Outlines of Classification," p. 407. 



88 



PLANT LIFE. 



upper angle formed by the leaf with the stem. This angle 
is known as the axil of the leaf, and such buds are said to 




Fig. 98. 



Fig. 98. — I, terminal shoot of an elm. A, leaf- 
scars; k, axillary buds. Natural size. II, 
one of the buds cut lengthwise through 
center, magnified 3 diam. a, young axis; 
.", li-.it -.car; bl, youDg leaves; </■ bud-scales. 
_ — After Behrens. 

Fig. 99. — .-) , twig of red maple with ac- 
cessory buds in addition to axillary bud. 
B, twig ol butternut, with leaf sear. «;. small 
axillary bud./', and larger accessory buds, 
1. d, above axil. Natural size. — After 
Gray. 

Fig. 100.— A bit of stem of a honeysuckle 
(Lonicera tylosteum) bearing large axillary 
and smaller superposed accessory buds 
above the axils of the scars, « >i, from 
which leaves have fallen. Natural size. — 
After Frank. 




be axillary (fig. 98). Ordinarily a single bud arises in the 
axil of each leaf. Its origin is always subsequent to that of 

the leaf- fundament (figs. 95, 96). 



THE SHOOT. 89 

There are many cases in which the lateral buds are not 
found precisely in the axils of the leaves, but slightly to one 
side, or at a greater or less distance above the axil (figs. 99, 
100). 

106. Extra-axillary buds. — Buds are frequently formed 
without any relation whatever to the leaf-axil, and even on 
the leaf itself (fig. 293). Sometimes these extra-axillary 
buds are produced without the action of any extraordinary 
cause, but more commonly injury of one sort or another 
seems to act as a stimulus to the production of such buds. 
Buds which do not originate in acropetal succession on the 
parent shoot are called adventitious buds. 

107. Adventitious buds may arise upon stems, leaves, or 
roots. They are most commonly and abundantly produced 
upon stems and roots. In the willows their ready production 
is utilized for obtaining young, vigorous, and pliable shoots 
to be used in basket-work. The few plants which produce 
adventitious buds upon leaves, as well as the many which 
produce them on stems, are often propagated in this way. 
(See m 364-) 

108. Dormant buds. — Many buds continue to grow with- 
out interruption from the time of their formation, but more 
cease to develop after they have reached a certain stage. 
Such buds may remain dormant for a considerable period, 
and may even be overgrown and completely enclosed by the 
wood upon old shoots. The bud in this case grows slowly 
and maintains itself near the surface of the wood. It is quite 
possible that these dormant buds should for some reason 
begin to develop later, when they are liable to be confounded 
with adventitious buds. In case they have been buried by 
the growth of tissues over them, the shoot which they pro- 
duce will seem to come from the interior of the organ upon 
which they are borne. This apparent internal origin must 
not be confounded with the real endogenous origin of roots. 



90 PLANT LIFE 

Since in most cases lateral buds have a definite relation to 
the leaves, the shoots which arise from them will have a 
similar relation. But, since many buds are produced which 
never develop into branches, this relation is often obscure 
and difficult to see. 

109. Special forms. — The primary shoot may'grow under- 
ground, in which case its stem usually takes a horizontal 
direction and becomes much thickened for storage of reserve 
food (•; 236), while its leaves are so reduced as to be scarcely 
recognizable. Such a shoot is known as a rhizome. When 
the primary stem is short, erect, and crowded with thickened 
leaf bases it forms a bulb, as in the hyacinth and onion. 
When the primary stem is short and thick, and has thin scale 
leaves upon it, it forms a conn, as in cyclamen and Indian 
turnip. 

Branches of the specialized primary shoot may be like it, 
as when some branches of the rhizome or corm are them- 
selves rhizomes or corms. Others, however, will be adapted 
to other purposes, as when aerial branches arise from rhizomes 
to carry foliage and flowers, or when slender leafless shoots 
called runners develop from the main axis of the strawberry 
(fig. 297). Offsets and stolons (figs. 296, 369) are similar 
branches likewise adapted to propagation (^[ 366). 

Branches of the secondary shoots may also be different 
from their parent axis. In different plants the shoots assume 
the most varied forms. 

Such specialized branches may be confined to a definite 
region of the plant, or may he distributed over it. The 
more important of these kinds of branches may now be 
enumerated. 

110. (a") Dwarf branches. — It is not uncommon to find 
branches specialized merely by their slight development in 
length and their capacity for being separated readily from 
the parent shoot. Such short branches are particularly com- 



THE SHOOT. 



91 



raon among the cone-bearing trees. In these plants the 
snort branches carry the clusters of needle leaves (figs. 10 1, 




Fig. ioi. — A shoot of Scotch pine showing two regions of dwarf branches each with a 
pair of needle leaves, and three regions oi flower branches; the flowers have fallen 
From lower two, showing scale leaves covering the stem, Naiur.il size.— After Will- 
komm, 



102, 358). After the death of the Leaves the branches 
themselves drop off. Somewhat similar short branehes are 



9 2 



PLANT LIFE. 



to be recognized among many deciduous trees, and, in the 
apple, the so-called fruit spins arc 
not dissimilar (fig. 103). 

111. (/) Flowers. — The most 
common of the specialized branches 
among the seed plants are those 
which constitute the flower. In 
these the axis usually remains short, 
the leaves are crowded, and often 





Fig. .02. Fi . .03. 

Fig. 102. — The base of leaves and dwarf branch of Scotch pine cut through the center 
lengthwise. Besides the two needle leaves the dwarf branch carries a number of scale 
leaves, d. Between the 1 ases of the needle leaves is seen the conical apex of the dwarf 
branch, showing their lateral origin. Magnified about 4 diam. — After l.uerssen. 

FlG. 103. — Twig of apple, bearing fruit spurs. A, points at which fruit was detached 
the preceding year ; // ', leaf scars. Natural size.— After Hardy. 



some of them are highly colored (fig. 104). 
these flower branches are deciduous. 



Commonly 





Mag- 



Pic;. 104. Fig. 105. 

Fig. 104. — Flower of Sedum acre, s, sepal; /, petal; si, stamen; c, carpel 

nified 3 diam— After Uaillon. 
FlG. 105. — Piece of a twig nf asparagus ; in the axil of the scale leaf, b, arise a (lower 

shoot, and three leafless needle-like branchlets. Magnified about 2 diam. — After Frank. 

112. (c) Cladophylls. — A few plants have developed 
shoots which replace leaves in function and resemble them 



THE SHOOT. 93 

In form. These cladophylls may be either broad and flat- 
tened, as in the "smilax" of the greenhouses, or they 
may be slender and needle-like, as in the common garden 
asparagus (fig. 105). In any case, since they replace leaves 
in function, they are abundantly supplied with green color- 
ing matter for manufacturing food. 

113. (</) Bulblets. — Other branches remain undeveloped 
as buds, but their leaves become thick and fleshy. These 
bulblets are easily detached and serve for propagation. (See 
^| 364.) They are to be found in many plants. In the 
tiger-lily they occupy the axils of the leaves (fig. 294), 
and are modified lateral buds, while in the garden onion 
they usually replace the flowers. 

114. (c) Tubers. —Some underground shoots have their 
ends suddenly and greatly enlarged, adapting them to the 
storage of food. They are then called tubers. In the white 
potato the tuber consists of several terminal internodes of 
an elsewhere slender underground stem, the "eyes" being 
lateral buds in the axils of minute scale leaves. In a few 
plants tubers may even be formed above ground, as in certain 
polygonums whose flowers are often replaced by little tubers 
which are readily detached (fig. 106). 

115. (/) Tendrils.— Some shoots take the form of slender, 
leafless, sensitive tendrils, which assist the plant in climbing 
by coiling about suitable objects (fig. 107). 

116. (g) Thorns. — Many plants produce defensive shoots, 
which are leafless, rigid, short, and sharp, called thorns, 
which may be either simple or branched (fig. 108). The 
honey-locust furnishes an excellent example of branched, or 
compound, thorns. 

Leaves themselves may be developed as tendrils or as 
thorns, so that it must not be assumed from appearance alone 
that such members are forms of the shoot. Observation of 
the origin and relation of the members will reveal their true 



94 



PLANT LIFE. 



nature. If shoots, they will usually be subtended by a leaf; 

if leaves, they will often have a bud or a shoot in their axils. 
Thorns or tendrils which do 
not arise at the nodes are 
reckoned as shoots. 

117. Duration. — Shoots are 
either annual, biennial, or per- 
ennial. If the entire shoot dies 





Fig. 106. 

Fig. 106.—.-!, upper part of a plant of Polygonum viviparum, showing flower cluster, 
the flowers in lower hall being replaced by tubers. Two-thirds natural size. /.', a 
fallen tuber. Magnified about 3 diam. C, a plantlet growing from tuber. Natural 
size.— After Kn ni 1 

Fig. 107. — A portion of the stem of white bryony, />', from which a tendril, ».>-, arises 
near the leaf stalk, />, and the bud, k . 11, rigid portion of tendril ; the portion between 
11 and tlu- portion .1, clasping the support. A, has become coiled into a spiral which 
reverses the direction oi the coils at w and «/'. Nearly natural size.— After Sachs. 

this generally involves the death of the whole plant, though 
new adventitious shoots may arise from the roots, as in 
sweet potatoes. In many plants, in which the shoot seems 



THE SHOOT. 95 

to die at the close of the growing season, an underground 
portion really survives, and sends up the new shoots. Such 
plants, if they live for two years, are called biennials ; or, 
if they live for several or many years, are called perennials. 




Fig. 108. — Shoots of Vella sfiinosa, showing thorns. Natural s 



The shoot may be composed mainly of soft tissues, and 
persist underground, where it is protected against unfavorable 
conditions, such as drought and cold, and especially against 
sudden changes; or it may be composed mainly of mechan- 
ical tissues, and be fully exposed, as are the shoots of trees. 
In these cases the leaves generally perish and drop off an- 
nually, but in the "evergreen" plants they live more than 
one growing season. 



CHAPTER IX. 

THE STEM. 

118. Definition. — The shoot is almost always segmented 
into members of two kinds, the stem and leaves. The stem 
is the central axis of any shoot, and the leaves are lateral out- 
growths, or branches, of it. These two members cannot be 
accurately defined, but are in most cases readily distinguish- 
able. Leaves commonly differ from the stem in internal 
structure, and in their flattened form, limited growth, and 
position, subtending the lateral shoots. (See further p. 117.) 

119. Nodes and internodes. — Upon examining the surface 
of the stem, it is almost always readily distinguishable into 
distinct regions, the nodes and internodes. The nodes are 
the narrow zones, often somewhat swollen (whence the name), 
at which one or more leaves arise. The internodes are the 
zones between the nodes. Upon watching the development 
of the stem from the terminal bud, it will be seen that new 
nodes and internodes are constantly emerging from its base, 
and that the leaves formed at the nodes are successively 
expanding. This emergence of the internodes is due to their 
elongation. The amount of elongation, however, varies 
greatly in different plants, and even in different parts of the 
same plant. In many cases the internodes are considerably 
and uniformly elongated ; the leaves are then distributed 
along the stem at considerable and regular intervals. In other 
cases the internodes remain very short, and the leaves are, 

96 




THE STEM. 97 

therefore, crowded. They may be so crowded as to completely 

envelop the stem and hide it 

from view. This is well seen 

in the scale-like leaves of such 

plants as the pines (fig. 101), 

cedars, and arbor vitas (fig. 109). 

Or, certain of the internodes 

may elongate, while others 

remain undeveloped. For 

example, in the shepherd's- 

purse, the first internodes 

remain short, so that the lower 

leaves are Crowded intO a tuft FlG >°9—A shoot of arbor vita; or white 

cedar, showing scale leaves covering 
Of rosette; the following inter- stem - Natural size.— After Kerner. 

nodes are elongated, the corresponding leaves being scattered 
at regular intervals; while, still higher, the internodes are 
again shortened and the leaves brought into close clusters in 
the flowers. 

120. The consistence of the stem depends upon the relative 
amount of mechanical tissues which it contains. Stems may 
be designated as woody, solid, or fleshy, terms which need no 
further definition. 

121. The shape of the stem varies extremely in different 
plants. Very commonly the stem as a whole is looked upon 
as cylindrical, but, if carefully considered, it will be seen that 
the diameters of successive internodes at first become gradually 
greater, and, after maintaining this maximum for a time, grow 
gradually less. The stem is, therefore, a cylinder with more 
or less conical ends. If the attainment of the maximum 
diameter is sudden, and the diminution similarly sudden, the 
resulting stem will have the shape of a double cone. The 
modification of such a form into the spherical is not diftic nit 
to imagine. Striking illustrations of these extreme forms are 
to be found among the cactuses (fig. no). 



93 



PLANT LIFE. 



122. A section of the stem commonly presents an irregu- 
larly circular outline (fig. in). Occasionally the surface of 
the stem is fluted or channeled, and, if these grooves or 
channels be few and the corresponding angles prominent, the 
section of the stem is polygonal, with three, four, five, six, or 
more sides. 

123. Habit. — As to habit, stems are commonly erect when 
enough mechanical tissue is developed to render them suffi- 
ciently rigid to carry not only their own weight, but that of 





Jmw^ 



A B 

Fig. iio. — Cactuses, showing form. A, Cereus dasyacanthus. B, Echinocactus 
horizontalis. In both the clusters of spines arise from tubercles on the stems. 
Reduced. — After Kerner. 

the leaves and other members attached to them. Other stems 
lie flat upon the ground, to which they may or may not attach 
themselves by the development of secondary roots. Between 
these prostrate, or creeping, stems and the erect form every 
conceivable position exists. The direction of growth is deter- 
mined largely by the relation of the plant to gravity and light 
as stimuli. (See ■ •; 285, 287.) Other stems rise into the 



THE STEM. 



99 



air, not by their own rigidity, but by the development of 
special members for climbing purposes, such as recurved 
spines, tendrils, sensitive leaf stalks, or even by recurved 
normal branches. (See ^[^[115, 158.) Others wrap them- 
selves about objects of suitable size, and are called twining 
stems. (See • 291.) The direction of twining varies with 
different plants, but most commonly corresponds to the 
movement of the hands of a watch, the support being sup- 
posed to be in the center. 

124. Primary structure. — The origin of the stem-tissues 
has already been described. (See ^j 100.) 

In following the stem from apex to base it is readily 
observed that the structure changes as the parts grow older. 
It is possible, however, to select a point at which the stem in 




Fig. hi. Fig. i 12. 

Fig. hi. Diagram ol a transverse section of stem of Iberis amara, showing outline, 

and paired \ asi ular bundles. The bla< k is the xylem bundle : the gray is the phloem 
bundle. The outer line represents the epidermis : a circle including the bundles would 
mark the limits ol the stele, with its 1 entral pith : the cortex lies between the epid« in is 
and stele Vftei Ntfgeli 
Fig. 1 (2.— Diagram of a transverse section ol a palm stem The epidermis is represented 

by the outer line; the endodermis by the innei one, with the narrow CO It ex between 

them; the stele, with numerous bundles scattered through the pith, is within the 
endodermis. Alter Frank. 



all cases attains a definite development. This point is at the 
internode whi< h has just reached its full length. The struc- 
ture of the stem at this point may be designated as its primary 
structure. If a thin section be cul from such an internode, 



IOO PLANT LIFE. 

three definite regions may be distinguished, viz.: (i) the 

epidermis; (2) the cortex; (3) the stele (figs, in, 112). 

125. 1. The epidermis. — This is a single layer of cells 
forming the extreme edge of the section, being, therefore, the 
layer which covers the surface of the stem. Here and there 
maybe observed intercellular spaces, which permit communi- 
cation between the outside air and similar spaces in the deeper 
tissues of the cortex. These openings are usually bordered 
by two specialized cells, and are called stomata. The 
epidermal cells may be furnished with green chlorophyll 
bodies, or these may be entirely absent. 

126. 2. The cortex. — This region consists of several 
rows of cells, usually thin-walled and not in close contact, and 
hence abundantly provided with intercellular spaces. These 
cells usually contain many chlorophyll bodies, to which the 
green color common to stems is due. 

The innermost layer of the cortex abutting upon the stele, 
whose radial walls are suberized (^J 9), is usually specialized 
to form a distinct layer of cells. This layer is the endodermis 
(fig. 1 1 8). 

127. 3. The stele. — The central region is called the 
stele. It consists, as in the root, ordinarily of three parts. 
Its outer layer of cells is known as the pericycle (fig. 118). 
Within the pericycle are clusters of smaller cells, the cut ends 
of the vascular bundles. Occupying the space between the 
vascular bundles is the pith (figs, in, 112). 

These regions of the stem are subject to various modifica- 
tions. 

128. 1. The epidermis. — While the epidermis is usually 
a single layer of cells, it is sometimes increased to two or 
three layers. Stomata may be entirely lacking. This is 
especially the case in those underground and submerged 
stems in which the stomata would be useless. The cells of 
the epidermis are often prolonged into outgrowths of various 



THE STEM. 



101 



shapes, such as hairs, scales, and the like (figs. 113, 114; 
see also figs. 361-365). 

129. 2. The cortex. — In some plants the cortex under- 
goes an enormous development, forming in some tubers the 
greater part of the massive stem. 
In other plants the cortex under- 
goes such reduction that it con- 
sists only of two or three layers of 
cells. It very commonly enters 
with the epidermis into the for- 




FlG. 113 




Fig. 113. — Forms of hairs from Plectranthus. a, simple pointed hair; /•, stalked 
glandular hair; < , sessile glandular hair with secretion covering the two glandular 
cells. Highly magnified. — After De Bary. 

Fig. 114. — T-shaped hair of the wall-rlower [Cheiranthus). e, epidermis. Highly 
magnified. — After De Bary. 



mat ion of outgrowths, which are then known as emergences. 
These emergences may take the form of rounded elevations, 
producing a warty stem, or they may be sharp pointed 
and either straight or curved, forming prickles (figs. 115, 
116); or the emergence may be produced along a con- 
tinuous line, giving rise to wings upon the stem ; or the 
stem may be more or less covered with large pointed or 
angular elevations, called tubercles, as in some cactuses 
(fig. no). Very frequently the intercellular spaces of the 
cortex are greatly enlarged, forming air passages of con- 
siderable size. These passages may arise by mere separation 
of the cells of the cortex, or by the destruction of those in 
certain regions, or by a combination of these causes 
(fig. 117). In other cases the cortical cells, instead of 



PLANT LIFE. 



remaining thin-walled, may become greatly thickened in 
certain regions, or even throughout the cortex. These 





Fig. 115. Fig. 116. 

Fig. 1 15 —Prickles on the stem of a rose. Natural size.— After Prantl. 

Fig. 116.— A longitudinal section through a rose prickle in a young stage, showing Imu 

the sub-epidermal (cortical) tissues enter into the structure of the emergence. Magni 

fied 200 diam. — After Rauter. 




Fig. 117. — Transverse section of the Stem of Elatine, showing intercellular canals, r. 
Magnified about 15 chain.— After Reinke. 

mechanical cells are likely to be aggregated in clusters or 
strands, and serve an important purpose in strengthening 



THE STEM. 



103 



the tissues (fig. 118). In some cases vascular bundles arc 
found in the cortex outside the stele, when they are known 
as cortical bundles. 




Fig. 118.— Transverse section of the stem of a ground [>ine (Lycoiodium complana- 
tinu). The stele is enclosed by the endodermis, en\ />, pericycle; »'. xylem bundle; 
///, phloem bundle; cc', cortex, . '. mechanical tissue with thickened walls; <■/, epi- 
dermis. In the cortex a branch stele passing out to a leaf c.n the right is cut across. 
Magnified ioo diam.— After Sachs. 

130. 3. Stele. (</) Pericycle. — The pericycle is rarely 
wanting. It is much more frequently increased from one to 
several layers of cells. In this case it commonly differ- 
entiates into regions of mechanical cells with thick walls and 
small cavities and a region of thin-walled cells. These 
mechanical cells are either aggregated in strands opposite to 
the vascular bundles of the stele, or they constitute a com- 
plete zone around it. Many of the most valuable textile 
fibers, such as those of tlax, hemp, and ramie, are obtained 
from this region of the stem (fig. 1 19). 

131. (/') Vascular bundles. — In any section of the stem 
the number of vascular bundles in the central cylinder varies 
greatly, not only in different plants, but c\cn in different 
parts of the same plant. The bundles are commonly arranged 



104 



ri.AA'T LIFE. 



in pairs, a phloem (bast) bundle and a xylem (wood) bundle 
being placed side by side, thexylem occupying the side next 




Fitt. i ic).— Portion of a transverse section of the stem of flax, m, pith; //.secondary 
xyiern forming a woody cylinder; pk, phloem ; />, bundles of mei hanical tissue (fibers) 
among the thin-walled cells, tin- two sorts making up the cortex; ./, the epidermis. 
Magnified about J5 diam. — After Frank. 

P 




Fig. 120. — Transverse section of a bundle pair from the stem of .1 begonia. 'The shaded 
pari is the xylem bundle; the small irregular cells above are the phloem bundle; 
between them is a zone "t urmi.itiiii: 1 • inn tern), the stelar cambium, 

ulii. Ii extends also right and left oi the bundle pair. The radius of the section passes 
through (V; C, next the center. Magnified 150 diam.— After Haberlandt. 

the center of the stem, and the phloem the side next the 
surface (figs. 1 1 1, 120). The number and position of these 



THE STEM. 



105 



bundles is, however, subject to change. In some cases 
one of the strands surrounds the other. Commonly it 
is the bast which surrounds the wood, as in the fernworts 
(fig. 121). Sometimes independent phloem bundles are 




Fig. 121. — Transverse section of Selaginella, showing three steles, eacli composed 
of a xylem bundle surrounded by phloem. /, /, intercellular spaces in cortex, 
separated from the steles only by the large-celled endodermis The cells underlying 
the epidermis are thickened to form mechanical tissue. Magnified 150 diam.— After 
Sachs. 

found with which are associated no xylem bundles. In 
the phloem certain cells may develop into libers, which 
are not to be confused with the fibers occurring in the 
pericycle. Some of these, also, are valuable in the textile 
industries. 



io6 



PLANT LIFE. 



The paired vascular bundles within the stele occupy various 
positions, and for purpose of location may be spoken of as 
though single. If transverse sections of the stem are ob- 
served, they may be seen either in a single row, roughly 
parallel with the surface of the stem (fig. in), or in several 
concentric rows (fig. 122), or they maybe irregularly dis- 
posed throughout it (fig. 112). No one method ofarrange- 




Fig. 122.— Transverse section of the aerial stem of an onion (A Ilium Schoenoprasum). 
e, epidermis; ch, chlorophyll-bearing tissue of cortex; r, colorless tissue of cortex; 
C, c'. vascular bundles (xvleni bundles black, phloem bundles dotted); sr, mechanical 
tissues connected into a cylinder; m, pith; A, pith canal formed by destruction of 
1 ells. Magnified 30 diam. — After Sa< lis. 

ment is confined to any of the larger groups of plants, 
although the first is characteristic of most dicotyledons, 
while both the second and third methods are common among 
the monocotyledons.* 

* So many exceptions are found to these last statements that it is lust 
not to indicate the arrangemenl of the bundles by the terms dicotyle- 
donous or monocotyledonous, as has been commonly dune ; nor is it 
possible to maintain the terms exogenous and endogenous, which have 
long since become obsolete because misleading. 



THE STEM. 



107 



h likewise varies greatly in 

to different conditions of 

found enormously developed 



as in some tubers, such as 
In other plants, particularly 



132. (c) Pith.— The 1 

different plants according 
growth. It is frequently found 
in those parts of the stem which are used by the plant 
for storing its reserve food, 
the white potato and the yam. 
those growing in water, it 
suffers extreme reduction or is 
often completely wanting, in 
which case the bundles of the 
stele are in close contact, and 
the cortex usually shows a cor- 
responding increase. In other 
plants the cells constituting 
the pith are greatly thickened, 
so as to form a mechanical 
tissue. The thickened areas 
are usually either opposite the 
bundles, forming a strand 
closely adherent to their inner 
faces, or they may extend to 
the flanks of the bundles, thus 
forming an arc embracing 
each. Sometimes the thickened region becomes extended 
between the bundles and joins the corresponding mechanical 
tissues in the pericycle, or even those of the cortex, so as to 
enclose completely the individual bundles (fig. 123). In 
other plants the pith dies early and shrivels up. Very large 
canals may thus be formed through it, or it may even dis- 
appear entirely (fig. 122). Such early disappearance of the 
pith produces the hollow stem characteristic of the grasses, 
the sedges, and the various members of the sunflower family. 

133. Secondary structure. — Some stems retain throughout 
their entire existence the primary structure which has just 




Fig. 123. — Transverse section Ol .1 bundle- 
pair of Indian corn. r>, phloem bundle; 
1. %\g, s, r, xylem bundle: p. pith; /, 
an intercellular space formed by the 
tearing of some of the .xylem tissues. 
The bundle pair is surrounded by a 
sheath of thick-walled mechanical 
tissues. Magnified 235 diam. — After 
Sachs. 



io8 



PLANT LIFE. 



been described, undergoing only slight changes in the char- 
acteristics of the individual 
tissues which compose it. 
Thus, with age, there may be 
a thickening of the tissues so 
as to impart greater rigidity ; 
or the waterproofing of the 
exterior may be made more 
perfect. These and similar 
changes do not, however, 
materially alter the structure. 
This permanence of primary 
structure is particularly fre- 
quent in the stems of mono- 
cotyledonous plants. It has 
been observed also in some 
dicotyledonous plants; for ex- 
ample, in the white water lily. 
But the stems of the great 
majority of dicotyledonous 
plants, as well as the conifers, 
quickly lose their primary 
structure, adding tissues of 
considerable amount, so as to 
bring about a more or less 
striking rearrangement of the 
iun of first formed tissues (fig. 124). 
S^Xc^tg h ° n Atf^Tep1- 134 - Secondary meristem.- 

SftA strSft xiKSS This modification of the struct- 

^^r^r^V^Z^r;;,: "re of the stem is due chiefly 

SS^i&S. ^SSHSLH to the formation of one or two 

AftcrTsd,iri1 ' layers of actively dividing 

cells, which constitute secondary meristem or cambium, 

roughly parallel to the surface. When there are two, one of 




THE STEM. 



IO9 



the layers of cambium arises nearer the (enter, the other 
nearer the periphery of the stem. They are formed from 
existing cells which resume their power of active growth 
and division. The development of the tissues from the ex- 
ternal meristem, or cork cambium, results in the formation 
of the periderm, while the tissues arising from the internal 
meristem, or stelar cambium, form the secondary xylem and 
phloem (fig. 124). 

135. 1. The formation of secondary cortex. — As the 
cells of the external meristem divide, sometimes the outer 
segments and sometimes the inner ones differentiate into 
permanent tissues, while the other segment remains as an 
initial for the next division. Some of the secondary tissue 
thus produced lies outside of the generating layer, and some 
inside (fig. 127). The secondary tissues, as a whole, con- 
stitute the periderm. 








Fig. 125. — A bit of a transverse section of a young stem of Scutellaria silendens at 
the beginning of tin- formation .if periderm. <■, epidermis, some of its cells divided by 
tangential walls, c, cortex. See tie 126. Highly magnified.— After Haberlandt. 

FlG. 126.— Same as 125 but older. <•, outer half of epidermal cells; k, cork cells formed 
by tangential divisions of inner half of epidermal cell (fig. 125) which has become pk, 
the cork cambium; ,, cortex. Highly magnified.— Alter Haberlandt. 

136. Periderm. — -The tissues formed inside the cambium 
{phellodernt) are usually similar to the cells of the primary 
cortex. They form intercellular spaces, and retain their 
living contents, among which chloroplasts are often present. 
W ith the thickening of the outer tissues, however, these 
usually disappear. 



IIO PLANT LIFE. 

The outside tissues of the periderm rarely remain living 
No intercellular spaces arise between the flat cells, which 
early lose their contents, while the walls become waterproof. 
Such a tissue is known as cork (fig. 128). Other cells may 
be altered into mechanical tissues by the thickening of their 
walls and the death of the protoplasm. Zones of cork often 
alternate in the periderm with zones of mechanical tissues 
Since no water solution can pass through a cork zone, it is 
evident that all parts lying outside of one are cut off from a 
supply of nourishment, and must therefore perish sooner or 
later. 

137. Location of cork cambium. — How much will thus be 
killed depends upon the position of the layer of cells which 





Fig. 128. 

Fir.. 127. — Part of a transverse se< don through the cork cambium and the tissues ii pro- 
duces in the European elm. k, cork cells, the innermost layer still with some proto- 
plasmic contents; pk, cork cambium; pd, secondary cortex. Highly magnified. — 
\1te1 Haberlandt. 

Fig. 128.— Part of a transverse section of young stem of cherry, showing formation of 
periderm, e, epidermis; k, cork; ///. cork cambium, with one row of secondary 
cortex below; ,, cortex. Highly magnified. — After Haberlandt. 



becomes the generating layer. It may be formed in one 
of three places: (a) It is sometimes in the epidermis itself 
(fig. 125), in which case only the outer half of the epidermal 



77//-; STEM. HI 

cells will be sloughed off.* (/>) In a majority of cases the 
generating laver of the periderm is formed in the cortex, 
either immediately under the epidermis (fig. 128) or in one 
of the deeper layers (fig. 127). (c) In other instances the 
generating layer is formed in the pericycle. If the pericycle 
is more than one layer of cells thick, it may be formed in 
the innermost or in any one of the external parts. In this 
case, therefore, there will be killed all the tissues of the 
cortex and any of the stelar tissues which lie outside the 
portion of the pericycle from which the generating layer is 
formed. 

138. Perennials. — Plants which live for a single year have 
usually but a small amount of periderm formed, or sometimes 
none at all. In those, however, which are perennial, peri- 
derm is formed not only during the first year's growth, but 
the activity of the generating layer is resumed at the begin- 
ning of succeeding seasons, so that annual additions are 
made to it. In the cork oak, for example, there is an extraor- 
dinary development of cork, which becomes so thick and 
is so resistant to the passage of water that it serves for the 
manufacture of stoppers. In the bottle-cork mechanical 
tissues occur, not in zones, but in isolated patches, forming 
the gritty masses in poor corks. 

139. Secondary periderm. — The dead tissues which accu- 
mulate from year to year upon the outside of perennial stems 
constitute a large part of what is known as the bark. In the 
bark of most trees one or more generating layers form in 
addition to the first, giving rise thus to secondary periderm 
(fig. 129). The secondary periderm may be either concentric 
with the first, in which case the outer parts of the bark will 
be made of concentric layers which separate readily from 
each other ; or the new generating layer may intersect the 

* The epidermis sometimes continues to grow for many years, while a 
secondary cortex is formed under it. In this case no sloughing oft occurs. 



112 PLANT LIFE. 

outer one, so as to isolate a mass of tissues of greater or less 
size. When this mass is killed by the formation of a sheet 
of cork on its inner face it gradually dries up and ultimately 
breaks away in the form of a scale or flake (fig. 129). Hark 
of this sort, such as that of the hickory, sycamore, or apple, 




Fig. 129. — Part of a transvn^ ■., ■< iii.ii <>f the bark of cinchona. c, layers oi <<>rk 
formed by a transient cork cambium. s, thin-walled tissues, with occasional stone 
cells. The sheets of cork cells are lines of weakness along which the flakes of bark 
split off. Magnified 665 diam. — After Warnecke. 



is known as scaly bark. In other trees the dead outer por- 
tions are persistent, and are only gradually worn away by 
the action of the weather. Such persistent parts become 
seamed or deeply furrowed lengthwise by the increased size 
of the stem within and the constant drying and shrinking 
of the dead parts. Such bark is called furrowed or ridgy 
bark. 



THE STEM. 113 

140. Lenticels. — In stems in which the generating layer 
of the periderm is formed from the epidermis or the cortex 
adjacent to it, the cork cells 
produced show certain modi- 
fications at points correspond- 
ing to the stomata of the 
epidermis. Here the cork 
cells become rounded and 
loosened from one another 
(figs. 130, 131). The epider- 
mis under the strain ruptures „ , , . . 

1 Fir,. 130. — A bit of a transverse section of the 

first at the Stoma, and exposes cortex of elder, showing a very young stage 

1 in the formation of a lenticel. 1 he cortical 

this powdery mass of cells c . el ,!, s imder a f " 1 ? hav f divi 4 ed tangen- 

1 » tially and are ionning a loose tissue which 

through a USUally biconvex > las already torn apart the guard cells 

' (See hg.. 131.) Magnified 120 diam. — After 

rift, whose shape suggested 8tahl - 

for the structure the name lenticel. Lenticels are formed 

either beneath single stomata, or, when the stomata are not 





^^k4oM 



Fig. 131. — Transverse section through .1 mature lenticel 
Compare fig. 130. Magnified 80 diam. 



uniformly distributed, beneath the clusters of stomata. When 
the generating layer of cork is deep-seated the lenticels pro- 
duced are without relation to the position of the stomata. 
141. 2. The formation of secondary wood and bast.- 
The position of the internal generating layer (the stelar cam- 
bium) is not subject to the same variations as the external 



ii 4 



PLANT LIFE. 



one. In stems of the few monocotyledonous plants which 
undergo secondary increase in diameter, the internal generat- 
ing layer arises from the pericycle. Upon division the inner 
segments, chiefly, differentiate, and from them arise new- 
isolated bundle pairs (in which the xylem bundle surrounds 
the phloem bundle) and new pith (fig. 132). 




Fig. 132. — Portion of a transverse se< lion of a stem ol Dracaena, in process of secondary 
thickening. <■, epidermis; I:, periderm; > . cortex, in which a bundle-pair 4 is passing 
out to a leaf : .1 . stelar i ambium ; ; . g, vas< ular bundles ; nt, primary pith ; tt, see on- 
dary pith. The amount of secondary thickening is shown by the radial arrangement 
of cells of secondary pith. Magnified about 50 diam. — After Sachs. 

In the many dicotyledons whose stems increase in diam- 
eter, the stelar cambium arises between the xylem and the 
phloem bundles of each pair, and extends across the pith 
rays which intervene, thus forming a complete zone nearly 



THE STEM 



115 



concentric with the surface of the stem (figs. 120, 124, 133^). 
As its cells divide, sometimes their inner, sometimes their 
outer segments differentiate into the tissues which they then 




Fig. 133. — Diagrams of transverse sections of stems illustrating modes of secondary 
thickening. In all c, cortex; in, endodermis ; />, pencycle ; ///', primary phloem ; 
ph.' , secondary phloem; cb, stelar cambium; .1 ', primary xylem; x", "secondary 
xylem ; >', primary pith rays; r", secondary pith rays.— After Van Tieghem. 

adjoin. Inside the generating layer between the bundles 
there arises, therefore, secondary xylem which becomes 
wood ; outside it, secondary phloem, or bast. Each bundle 
is thus increased in its radial dimension (fig. 124 ). 

142. Pith rays. — The generating layer in the pith rays 
arises from the pericycle or from some part more deep- 
seated, but in any case it connects directly with the generat- 
ing layer between the adjacent bundles (fig. 124). In this 
portion of the generating layer two distinct modes of develop- 
ment are to be observed : either the tissues produced by the 
division of the cells differentiate into pith tissue (B, fig. 133), 
or they form secondary wood and hast corcsponding to that 
produced between the adjacent bundles. In the latter case, 
therefore, a complete /one or ring of secondary wood and 
bast is formed, so that the pith occupies the center. Upon 
the ring of secondary wood thus produced the primary wood 
bundle projects into the pith, and upon the ring of secon- 
dary bast the primary bast bundle projects into the rortex 

(C, fig. 133). 



I l6 PLANT LIFE. 

Intermediate between these two methods, it is common to 
have new bundles produced by the differentiation of the 
secondary tissues formed in the pith rays, these bundles 
remaining separated by pith rays. In this case a xylem 
bundle is usually first formed, followed shortly by a phloem 
bundle outside (Z>, fig. 133). 

The secondary bundles thus formed can, of course, have 
no connection with those which enter the leaves. In this 
they differ from the primary bundles, branches from which 
enter each leaf. (See •[ 163.) 

143. Annual rings. — If the stem is perennial, year after 
year the stelar cambium resumes its growth, adding layer 
after layer to the secondary wood and bast. Thus most trees 
have their shaft-like trunks formed. The generating layer 
forms a line of weakness, especially when dividing rapidly, 
and the parts outside separate readily from the wood. They 
constitute the bark. 

144. 3. The bark. — As has been already shown, the 
outer part of the bark consists of the dead, dry, shriveled 
tissues of the periderm lying outside the cork cambium. The 
inner portions of the bark are composed of the tissues which 
lie between the cork cambium and stelar cambium. This 
inner part contains a greater amount of water than the outer, 
and always some living tissues. It may consist of a part of 
the cortex (depending upon the place of origin of the peri- 
derm), the pericycle, and the primary and secondary bast. 
As the tree grows older, the secondary generating layers of 
the periderm invade the cortex and the bast, until, with 
weathering, the bark may come to consist wholly of secondary 
bast. It attains considerable thickness only when the loss 
from this cause is slow. 



CHAPTER X. 

THE LEAVES. 

145. Primary leaves. — Leaves are distinguishable into 
primary and secondary. The primary leaves arise directly 
from the first cells produced by division of the egg. In the 
fernworts two of the octants into which the egg divides 
produce the primary leaf. This is entirely unlike the secondary 
leaves, which arise upon the sides of the stem. In seed 
plants, one, two, or more leaves develop as members of the 
embryo, only a I'ew plants (and those probably degenerate in 
this respect) not forming leaves before the embryo enters its 
resting stage. 

The primary leaves of seed plants are called cotyledons 
(figs. 134, 135). They are usually transient, and not rarely 
so distorted by acting as storage places for reserve food that 
they do not function as foliage leaves at all. In extreme 
cases of this kind they remain in the seed coats when the 
embryo resumes its growth, as in pea and oak. 

146. Secondary leaves are generally numerous and much 
more conspicuous. It is these which are usually meant by 
" leaves," unless primary leaves are specially named. 

147. Development. — If the apex of the shoot is examined, 
its progressive differentiation into stem and leaves can be 
observed. Upon the sides of the growing point swellings of 
various size appear, the smallest being nearest the apex (fig. 
95). These swellings are the fundaments of the leaves, into 
which they become transformed by further development. 
Similar swellings appear later just above the leaf fundaments, 



PLANT LIFE. 



which are at first not distinguishable from them, except by 
position (fig. 96). These become the branches. Both leaf 
and branch have their origin usually in the outer layers of the 
shoot, and can only be distinguished by the later course of 
development. The growth of the branch is commonly 
indefinite, while that of the leaf is generally limited ; the 




Fir.. 134. Fig. .35. 

Fig. 134 A seedling oJ wheat, with grain still attached cut through lengthwise, showing 

the single inim.iry li.it with its back applied to the store ot reserve food in the grain 
(the shaded part). The tirst two secondary leaves are also developing, and the primary 
root has extended. Magnified 4 diani Alter Kernel 
Fr<;. 135.— Seedlings, showing primary leaves. A, a fir (. Hies orientalis); />, the dog- 
rose; C, a morning-glory. Naturafsize. — After Kerner. 

branch usually develops leaves and often buds as lateral out- 
growths, while the leaf rarely forms buds normally ; the axis 
of the branch is generally radial, like the parent axis, while 
the leaf is generally flattened and dorsiventral. In most cases, 
also, the leaf subtends the branch, both leaf and branch 
mark those points of the stem known as the nodes. 



THE LEA VES. I 1 9 

148. Arrangement. — Leaves appear in regular succession 
upon the stem, the youngest being nearest the apex. Their 
distribution along the sides of the stem, though extremely 
various, may be reduced to two main types. Either (i) the 
leaves are formed singly at the nodes, or (2) more than one 
leaf occurs at each node. When the leaves are single, succes- 
sive leaves may stand upon exactly opposite sides of the stem, 
so that the third leaf, counting from below upwards, stands 
over the first ; or the fourth leaf may stand over the first ; or 
the sixth over the first, and so on. A transverse section of a 
bud shows the mode of arrangement, and a study of such 
sections makes it evident that each leaf appears in the widest 
space between the two preceding leaves, i.e., where it 
encounters the least resistance. That this is the determining 
factor is shown by the fact that the order of arrangement may 
be artificially altered by pressure or distortion of the bud. 
When two or more leaves occur at each node, the members 
of successive circles ordinarily alternate with each other. 
This alternation is due to the same cause. 

149. Form. — Leaves show a great variety of form and 
structure. Even upon the same plant leaves of various forms 
occur. The primary leaves are usually different from the 
secondary leaves, both in form and size. The most abundant 
form of secondary leaves is foliage leaves. These may be 
very simple, as the " needles " of the pines, or differentiated 
more completely, as in the deciduous trees. The mature form 
of the complex foliage leaf is frequently not attained until 
several nodes above the point at which the primary leaves 
arise; and, if only one or two leaves are produced each 
season, as in many ferns, the mature form may not appear lor 
several years. 

150. Foliage leaves. — A well-developed foliage leaf may 
usually be divided into two equal parts by a plane passing 
through its base and the axis of the stem to which it is 



120 



PLANT LIFE. 



attached, i.e., it is bilateral. Moreover, the upper and under 

surfaces are usually different, i.e., it 

is dorsiventral. It has three parts, 

the base, the stalk, the blade (fig. 

136). The leaf base is always 

present, but either the leaf stalk or 

the leaf blade or both maybe absent. 

The leaf blade is ordinarily winged ; 

indeed it is for this reason that il 

W-i 




Fig. 136. Fig. 137. 

Fir,. 136.— Leaf of Ranunculus Ficaria. /-, leaf base; /.petiole, or leaf stalk; /, 

lamina or leaf blade. Natural size. — After Prantl. 
Fig. 137. — A leaf of a grass, with part of stem to which it is attached, s, sheath (leaf 

base)attached all around node k of the stem //, /; ; /, blade ; /, the ligule, an outgrowth 

from the surface. Natural size. — After Frank. 

received the name " blade." Either the stalk or the base or 
both may also be winged. 

151. 1. The leaf base. — The leaf base is generally en- 
larged so as to form a sort of cushion by which it is attached 
to the stem. When a broad base is attached over a consider- 
able arc of the circumference of the stem, so that it encircles 
it more or less, the base is said to be sheathing (fig. 136). 
In grasses, for example, the leaf base is attached over the 
entire circumference of the stem, and enwraps it completely 
for a considerable distance above the node (fig. 137). 



THE LEAVES. 



121 



152. Stipules. — The leaf base frequently branches. These 
branches, commonly two in Dumber, arc called stipules (fig. 
138). They vary from slender, awl -shaped bodies to flat- 




Fir,. 138.— A growing shoot of a thorn (( 'rateegus punctata), n, leaves developed as 
bud scales which protected the parts above when in the bud; .V, stipules. Natural 
size. — After Reinke. 



tened and leafdike ones. The stipules may remain attached 
to the base throughout the life of the leaf, or may fall away 
early. Usually the two are separate, but they may be united 
with the leaf base itself, forming wings for it, as in roses 
(fig. 139), or they may be united with one another so as to 
form a sort of sheath encircling the stem (fig. 140). When 
the leaf base is winged, the wings extend downward as lobes 
more or less encircling the stem. In many cases the leaf is 
said to be clasping (fig. 141 ). These lobes may even unite 
on the other side of the stem, so that the stem seems to 
penetrate the base of the blade. (See fig. 142.) When two 
leaves occur at the same node, corresponding lobes of the 



PLANT LIFE 



leaf bases may unite, so that the stem seems to pass through 
the center of a leaf which extends equally on each side of 
it. (See fig. 143.) 




Fig. 139— A young flowering shoot of dog-rose, showing various forms of leaves and 

transition from one to the other. «'-«*, scale leaves; Z 1 -/ 3 , foliage leaves; A'-A*, 

- hracts ; the flower leaves not clearly shown. The scale leaf, «', shows a leaf base, 

winged by stipules b, with only a trace of stalk and blade,;. Trace these parts into 

foliage leaves, where the blade becomes compound, and subsequent reduction through 
the series oi bracts. Natural size. — Alter I.uerssen. 

153. 2. The leaf stalk.— The leaf stalk is also known 
as the petiole. Its form is more or less cylindrical, usually 
with a groove or channel upon the upper side. Sometimes 
the petiole is flattened in a vertical plane, a.s in aspen poplars. 



THE LEAVES. 



23 



When this flattening is extensive, so that the petiole becomes 
thin and leaf-like and the blade is wanting, it functions as a 
foliage leaf (fig. 144). Not infrequent- 
ly, the petiole is winged, as in the orange. 
It may be entirely wanting, in which 
case the blade arises directly from the 
base, as in most grasses 

(fig- 137). 

154. 3. The leaf 
blade. — To this part of 
the leaf the word ' ' leaf ' ' 
itself is frequently ap- 
plied. In general, the 
:he leaf blade is so broadly 
winged as to be thin and 

clasping base. flat . but ^ gradations 




she. uli 



forming 



Potygvnu 

above the sheathing leaf base . 
cut-off leaf f: cc, the stem; ca, an axillary 
shoot. Natural size. — Alter Frank. 
FlG. 141.— Leaf of Tklaspi 
Natural size. — After Prantl 





Fig. 142. Fir.. 143. 

Fig. 142. — Shoot of Uvularia, showing perfoliate leaves below. About half natural 
size— After Cray. 

Fig. 143. — A shoot of wild honeysuckle, showing upper leaves connate-perfoliate. 
About half natural size.— After ( Iray 



124 PLANT LIFE. 

exist between such forms and those that are much folded or 
crumpled, thick and fleshy, oi even cylindrical. 




Fig. 144.— A shoot of Acacia, showing at a a twice-branched (compound) leal with 
roundish petiole ; at 6, a similar leaf with flattened blade-like petiole ; at c, phyllodia, 
i.e., blade-like petioles without true blades. About half natural size (?). — After Frank. 

If a thin blade be held between the eve and the light, two 
parts become evident : (i ) a green tissue (mesophyll), more 
or less opaque ; and (2) translucent "nerves" or " veins." * 
The larger of these, usually called the " ribs," * frequently 
form ridges upon the under surface.")" 

155. Branching. — The outline of the blade is extremely 
various. It is dependent upon the character and extent of 
its branching, which may be either slight or extensive. 
Slight branching gives rise to teeth of various forms (fig. 

* These words must not be thought to indicate any resemblance in func- 
tion to the same parts in animals, but only similarity of position or ap- 
pearance. 

f For further account of structure see ^[ 168. 



THE LEAVES. 



125 



145). More profound branching is evident 'in divided or 
parted leaves (fig. 146). In 
some blades the branching 
is so extensive and complete 




Fig. 146. 
) , leaf with crenate edge ; />', leaf with 



ARC 
Fig. 145- 
Fig. 145.— Diagrams of slight leaf branching 

dentate edge ; C, leaf with serrate edge. — After Bessey 
Fit;. 146. — Leaf of A morphophallus, showing sympodial branching. Th 
lateral axes are numbered in order. The extent of branching makes the blade divided. 
Reduced. — After Sachs. 

that the green tissue no longer fills the intervals between the 
larger ribs, but the blade is made up of a series of independ- 
ent portions united to a common stalk. Each ultimate 
branch of the blade is known as a leaflet. Blades in which 
the green tissue is continuous, even though deeply divided, 
are called simple leases. (See figs. 136, 138, 141, 142, 145, 
146. ) Those which are segmented into leaflets are called 
compound leaves. (See figs. 139, 144, 147, 148, 141).) 

156. Venation. — The mode of branching of the blade is 
indicated by the main ribs which occupy the axes of growth. 
(See ^1 169.) Study of distribution of the ribs and veins of 
the blade, that is, of its venation or nervation, shows that 
monopodial branching (*T 93) is the common mode, sympo- 
dial branching occurring rarely (fig. 146). The arrangement 
of the larger ribs may be reduced to two main types.* (1) 



* Compare mode of branching of shoot, " i".;. 



126 



PLANT LIFE. 



There may be a main rib, from whose flanks arise at regular 
intervals a series of lateral branches which may themselves 




Fig. 148. Fig. 149. 

Fig. 147.— A palmately branched (compound) leaf of horse chestnut. About one-fifth 

natural size.— After Bessey. 
I'ii.. 148. — A palmately branched (compound) leaf. — After ISessey. 
FlG. Mi).— Leaflets of maidenhair fern showing dichotomous branching of veinlets, 

which end free. Natural size. — After Ettingshausen. 

again be branched in various ways. Such a leaf is said to be 
pinnaiely veined (figs. 138, 151, 153). Or (2) from the top 
of the petiole several large ribs of almost equal strength may 
be given off. Such venation is palmate (figs. 150, 152). 
These may be parallel (fig. 150) or radiate (fig. 152). 

The distribution of the small veins or nerves shows three 
types. They may either (1) connect with each other so as 
to form an irregular meshed network (fig. 151); or, (2) leav- 
ing a rib nearly at right angles, they may run parallel with 
ea< h Other to join another large vein ; or (3) they may leave 



THE LEAVES. 1 27 

the large vein and end free (fig. 149). In the first type the 
finest branches of the veins, too delicate to be seen without 
the microscope, often end free in the meshes formed by the 
next larger branches (fig. 164). Near the margin of a blade 




Fig. 150. Fig. 151. 

Fig. 150— Parallel venation of leaf of Polygonatum latifolium. Natural size. — 
After Ettingshausen. 

Fig. 151. — Pinnately netted venation of leaf of a willow. Natural size.— After Ettings- 
hausen. 

the larger veins are often so connected with each other as to 
form one or more series of arches whose convex side is 
directed toward the margin. These forma sort of selvedge 
and protect the leaf against tearing (fig. 153). 



128 



PLANT LIFE. 



157. Special forms. — Foliage leaves may be modified to 
serve special purposes without wholly losing their function as 




Fig. 152. — Palmately veined and branched leaf of Norway maple. About half natural 
size. — After Kerner. 

foliage. For example, the petiole may be made sensitive to 

contact and adapted to wrap about slender objects, like a 

tendril, as in clematis and j^fs, *t 

nasturtium (fig. 154). Such 

plants are called leaf-climb- — ' v 

ers. 





Fig. 154. 

Fir.. 153 .— Pinnately veined leaf of buckthorn, with looped ribs forming a selvedge. 

After Kerner. 
Fig. 154.— Portion of a plant of the dwarf garden-nasturtium {Trofiaolum minus). 

The long petiole a, ,*, ,1 of the leaf / is sensitive to contact and has coiled about 
the support and its own stein, st. ~, axillary branch. Natural size.— After Sachs. 



THE LEA VES. 



2 9 



Some plants develop their leaves into the form of sacs or 
pitchers. These ordinarily represent the black- of the leaf, 
and are more or less urn- or trumpet-shaped. They may be 
either without petiole, as in Sarracenia (fig. 155); or 




A ••-;- 



Fig. 155. — Pitcher-plant {Sarracenia purpurea). Leaf above A cut off to show 
trumpet form. One-third natural size. — After Gray. 



petioled, as in Utricularia | figs. 383, 384) ; or the petiole 
may be winged to serve for foliage, as in Nepenthes ( fig. 
382). A few plants have their leaves modified so as to serve 
as traps, which, by their sudden movements, capture small 
animals (figs. 386, 387, 388). 

But generally the foliage function is subordinated to the 
other work, and the leaf takes on peculiar forms, the more 
important of which are as follows : 



i 3 o 



PLANT LIFE. 



158. (i) Tendrils. — The leaf blade alone, or some of its 
branches, or the petiole and blade, may develop as a cylin- 
drical body, without wings and sensi- - ,, 
live, known as a tendril. In the pea, ^^ I^U* 
the stipules become very large, and 
take the function of the reduced blade 
(fig. 156). In other plants the base 
may be broadly winged for the same 
purpose. 





Fig. ,56. 

Fig. 156.— Portion of shoot of pea, with a pmnatcly compound leaf whose upper leaflets 

are modified into tendrils and the stipules greatly developed to serve as foliage. 
About half natural size.— After Frank. 
Fir.. 157. — Piece of the stem of locust {Robinia Pseudacacia), showing stipules in the 
form of thorns. Natural size. — After Kerner. 

159. (2) Thorns. — The leaves may develop into slender 
conical and sharp-pointed thorns or spines, either branched 
or unbranched (fig. 390). Sometimes the stipules alone 
become thorns, as in locust and acacia (fig. 157). Neither 
tendrils nor thorns can be distinguished structurally from 
similar forms of the shoot. 

160. (3) Scales. — In buds, on underground stems and 
on various parts of the aerial stem, are found small, scale-like 
leaves of various shapes (figs. 101, 102, 105, 109, 138, 139, 



THE LEAVES. 13 ' 

358). These scales may represent the sheathing base only ; 
they may be the base with the stipules (fig. 139); or they 
may represent the leaf base and the blade. The petiole in 
all cases is wanting. In addition to the modification of 
form, scales, especially those that are protective, have their 
tissues firmer and more resistant to cold and unfavorable 
external conditions. Not infrequently the scales are covered 
with secreting hairs, or possess glands sunk beneath their 
surfaces, whose function is to produce and excrete resins and 
similar materials. The inner protective scales of buds (fig. 
98) are often covered with an abundant coating of woolly 
hairs, which serve to prevent rapid change of temperature in 
the interior of the bud. 

161. (4) Flower leaves and bracts. — -On certain parts of 
the stem, leaves are commonly profoundly modified to carry 
the spore cases. They are called sporophylls (c, si, fig. 104). 
(See ^[ 329.) Adjacent to these are others which may be 
highly colored and adapted in form to protect the sporo- 
phylls, and to facilitate the visits of insects (s, p, fig. 104). 
A shoot whose leaves are thus clustered and specialized con- 
stitutes a " flower." The leaves adjacent to the flower leaves 
are also more or less modified in form and reduced in size. 
They are called bracts (// •> 2 > 3. fig. 139). (See also ^[ 359.) 

162. (5) Storage leaves. — Other leaves are utilized for 
purposes of storage. For this purpose the ribs are reduced in 
number and size, while the softer tissues of the leaf are often 
enormously developed, and serve as the receptacles of the 
reserve food. The primary leaves of the seed plants (coty- 
ledons) are often much distorted by the deposit in them of 
reserve food for the embryo. When such leaves possess 
sheathing bases the structure resulting from the union of a 
number of such leaves upon a short axis is called a bulb. 
(See also ^f 109.) The leaves of buds are sometimes thick: 
ened by the deposit of food material, and when such buds 



132 PLANT LIFE. 

loosen from the plant they may produce a new plant, as in 
the tiger-lily (see ^[ 361-364). Both base and blade may be 
used for storage, as in the century-plant j or the entire leaf 
may serve the same purpose, as in the cultivated cabbage. 

163. Structure. — Three regions in each part may be dis- 
tinguished, as in the root and stem : (1) the epidermis ; (2) 
the cortex ; both continuous with that of the stem ; (3) the 
Steles, continuous with those of the stem when the latter 
contains several steles, or branches of it when the stem con- 
tains a single stele. 

164. (a) The petiole. — The structure of the petiole agrees 
in all essentials with that of the stem (see % 124 {{.). The 
epidermis forms the outer surface, frequently with hairs or 
emergences (see ^[128, 129). The cortex consists of 
rounded or cylindrical thin-walled cells, the outer layers 
containing chlorophyll, and frequently with angles much 
thickened for strength. Mechanical tissues forming strands 
or bands are also frequently present in the cortex. In water 
plants, e.g., in water-lilies, large intercellular chambers, 
often forming extensive canals, arc present. There may be 
a single stele, surrounded by an endodermis and containing 
several or many vascular bundles (B, fig. 158); or there may 

A />• 




Fig. 158. — Diagrams of transverse sections of petioles shoving two most common 

structures. A, petiole with several steles, /.'. petiole with one stele, containing a 
number of bundle pairs. ,. cortex; en, endodermis; ///, phloem; jr, xylem ; 
in. pith ; ' , pith rays I he letters .1 , B stand on the upper or ventral side of petiole. 
— After Van Tieghem. 

be several steles, each surrounded by a special endodermis 
and consisting of little more than a pair of vascular bundles 



THE LEAVES. 



133 



(A, fig. 158). In transverse section the vascular bundles 
are variously placed, being irregularly scattered, or disposed 
in one or several groups. The single group is most common, 
with the paired bundles placed so as to form a crescent, or 
even a complete ring, which is flattened above or triangular. 
The largest pair is generally median and dorsal (fig. 158), 
with smaller ones right and left. 

165. (b) The blade. — In broad leaves, the epidermis of 
the blade is made up of tabular cells, often with wavy lateral 
walls (fig. 159). In narrow leaves the epidermal cells are 




Fig. 159. — Surface view of epidermis from under side of leaf of bracken fern {/'let is), 
showing wavy cells, except over veins, v, where they are elongated, st, stomata. 
The dot in each cell represents the nucleus. Highly magnified. — After Sedgwick and 
Wilson. 

longer than wide (fig. 160). Over the veins the (ells are 
elongated parallel with the vein. The epidermal cells are 
generally free from chloroplasts. The epidermis usually 
consists of one layer, but in some plants becomes several 
layered, either to serve as additional protection against eva- 
poration or for use as a water-storing tissue. ( See • 441. ) 



'34 



PLANT LlfE. 



Hairs of many sorts, plain, stinging and glandular, and 
of various sizes, arise from the epidermis (figs. 361-365). 
They are essentially like similar structures on the stem (figs. 
113, 114). 

166. Stomata. — Numerous intercellular spaces bounded 
by a pair of specialized cells, called guard cells, penetrate 





Fig. 160.— Surface '.iew of epidermis from the leaf of oat, showing elongated cells (more 
elongated over vein, >i, >:) and stomata arranged in lines. Moderately magnified. — 
After Frank. 

Fig. 161. — Perspective view of a stoma from the under epidermis of the beet leaf, show- 
ing the sloping sides of the slit, the crescentic guard cells with chloroplasts. Highly 
magnified.— After Frank. 

Fig. 162.— Sections through stomata of beet at right angles to their length. The upper 
figure shows the stoma open ; the lower closed. The black line represents the primary 
wall, to which additional material, especially in the guard cells, has been added. 
These thickenings serve by their elasticity to close the stoma. Opening is dm- to 
turgor "i the guard cells The chloroplasts and granular protoplasm are shown. 
Highly magnified. Alter Frank. 

the epidermis. The whole apparatus is called a stoma (s/, 
fig. 159, 160). The guard cells are crescentic, sometimes 
with enlarged ends (fig. 160, like curved dumb-bells then), 



THE LEAVES. I 35 

and arc sensitive to various external conditions, especially 
light, so as to control the size of the slit-like space between 
them by changes in their curvature (fig. 162). This slit is 
formed, like most intercellular spaces, by the partial splitting 
apart of the cells. It communicates with extensive intercel- 
lular spaces in the interior. 

The stomata are very numerous. In different plants, in 



the space here enclosed 



, the numbers usually vary 



from 4000 to 30,000, sometimes, however, reaching as much 
as 60,000 to 70,000 in the olive and rape. They are not 
equally jlistrihuted o nJ he two si des of the le af.- being usually 
mo re numerous j)n th e under^sidej where there arc nmrc in - 
ternal intercellular spaces.. They may be wanting on the 
upper side, as in lilac, begonias, and oleander. There are 
no stomata on submerged leaves nor on the under sides of 
floating leaves. In some plants they are found in clusters, 
in others uniformly distributed. 

167. Cortex. — -The cortex of leaves is called the meso- 
phyll. It consists of thin-walled, active cells, for the most 
part richly supplied with chloroplasts. In thick leaves the 
internal cells are without them. In some leaves the cells of 
the mesophyll are nearly uniform, but in most those near the 
upper surface are more elongated and close set, forming one 
or two rows, with their ends outward, while cells near the 
lower surface are irregular in form, with large intercellular 
spans. These tissues are known as the palisade and spongy 
parenchyma (fig. 163). 

About the steles, the cortex forms the usual endodermis 
{gs, fig. 163), and often develops along the larger into one 
or two strands or a sheath of mechanical tissues. These 
tissues, together with a stele, constitute the rib or vein, often 
so massive as to project beyond the other parts in thin leaves. 



136 



PLANT LIFE, 



168. Steles.- The steles are numerous and ramify through 
the blade. Their structure is essentially as described for the 












Fig. 163.— Diagrammatic vertical section of a leaf, 
and stomata sp, sfi. Between upper and lower epid 



pidermis, with cuticle c, c, 
the mesophyll, with cells 



ivii, 1 
abundantly supplied with chloroplasts. The upper row of elongated cells is the pali- 
sade parenchyma ; the rest form the spongy parenchyma, both with many intercellular 
mmunicating with outside air through stomata. In the mesophyll lies 
a small vein, here cut across, composed of a ventral xylern bundle v. a dorsal phloem 
bundle ,v, surrounded by the endodermis .;,*. and the pericyclc (between e and .!,•■»')■ 
After Sachs. 



stem (•] 127). Each of the smaller consists of little more 
than a single pair of vascular bundles. The xylem bundles 
alone form the last branches (fig. 164), the phloem disappear- 
ing earlier. The larger ribs may form one or two strands or 
a complete sheath of mechanical tissues by the development 
of the pericycle, and the bundles proper may be increased 
by the development of secondary wood and bast. (See 
■" 141. 



THE LEAVES. 1 37 

169. Growth.— The growth of the leaf is at first apical. 
In fern-worts its tissues are produced by the continued divi- 




FiG. i^. — A few meshes of the finest veins of a leaf of A nthyllis. »i , main vein ; />, />, 
branches ; <;. .;, .;. a closed mesh ; . . ends of the finest veins within the mesh. The 
drawing shows only the xylem bundles ; the phloem bundles accompanying them and 
the mesophyll cells filling the meshes are not shown. Moderately magnified. — After 
Sachs. 

sion of a single apical cell, and the further division of each 
of the segments so produced (/, fig. 76). The branches of 
such leaves, therefore, arise in acropetal succession. In most 
seed plants, instead of a single apical cell, there is a cluster 
of such cells. Growth at the apex often ceases early, and is 
replaced by growth throughout the whole extent of the leaf. 
This intercalary growth is sometimes localized between the 
fundament of leaf base and blade, producing the petiole 
when one is formed. In elongated leaves without distinct 
petiole, as in grasses and many other monocotyledons, a zone 
of growth occupies the entire base of the blade. By the 
division of these cells, chiefly at right angles to the length 



i.SS 



PLANT LIFE. 




of 



ith 



of the Made, its tissues are produced. In such plants apical 
growth ceases so early that it can 
be observed only in the youngest 
stages. 

170. Of branched leaves. — 
When the leaf is to become much 
branched, two or more new growing- 
points develop, so that each of the 
branches has at its apex a growing- 
point (fig. 166). These growing- 
points may arise from the apical 
growing-point, or from the basal 
one, or sometimes from both. The 
branches will appear accordingly 
the in acropetal or basipetal succession, 
the or even in both as they do in the 
The limits of the 
growing-point are even more in- 
definite than in the stem. The cells of which the leaf is 
composed are produced very rapidly, and at a very early 
stage division ceases. 

171. Wintering. — In those plants which live from year to 
year, producing new leaves each spring, the unfolding of 
these from the winter buds is due chiefly to the enlargement 
of cells already formed. New leaves are ordinarily produced 
before the close of the growing season preceding that in 
which they are expanded, and are protected in the winter 
buds. The partly developed leaves in the bud may be flat, 
but broad leaves are commonly folded or rolled in various 
ways. 

172. Growth limited. — The growth of the leaves is ordi- 
narily limited, rarely extending over a single season. In a few 
ferns and coniferous plants the leaves continue to grow for a 
longer time. Indeed, in the curious Welwitschia (fig. 167), 



Fir.. 1^.5. — Ending of a v« 
mesophyll of a leaf, t, 
spirally thickened cell 
xylem ; c, c, mesophyll cells win 

chioropiasts ; a, a, cells of the leaves of yarrow. 

endodermis. Magnified 230 diam 
— After Frank. 



THE LEAVES. 



1 39 



the basal growth of a single pair of persistent secondary 
leaves is continued throughout the long life of the plant, 
while the tips die and are frayed out. 

173. Production of the other members. — Leaves give rise 
under certain conditions to roots or to shoots. The number 
of plants, however, in which this occurs is comparatively 




FlG. 166. — Development of the pinnately compound leaf of the locust {Robinia Pseud- 
acacia). . I , young stage, snowing on one flank the first lateral growing-point,;, 
which is to produce the lowest leaflet. />', an older stage with the fifth growing-point 
x just showing. A sixth is still to be developed. The hairs in A and A' are on the 
back (under side) of the leaf, and drop off early. C*, nearly mature leaf. ./, /■', 
magnified; c, about i natural size.— After Frank. 

limited. Roots arise from leaves in precisely the same way 
as lateral roots arise from stems (•[ 95), that is, they arc en- 
dogenous in their origin, and develop always near the surface 
of the steles. 

When a leaf produces a shoot, it is from the epidermis or 
from the green tissue underlying it, never from the steles. 
Shoots thus arise from the part of the leaf corresponding to 
that from which branches arise upon the parent shoot. 

174. Secondary changes. — Leaves, like stems and roots, 
undergo certain secondary changes, hut these are neither so 



140 PLANT 11 IE. 

common nor so extensive as in the other two members. The 
formation of several to many layers of cork cells upon the 
surface of scale leaves is not uncommon. Occasionally simi- 
lar layers of cork are formed upon the petioles of ordinal) 



Fig. 167. — Welwitschia mirabilis, a coniferous plant of Africa, showing two leaves 
which grow at base and continue to develop throughout the many years which the 
plant lives. The tips are dead, and become worn and frayed by winds. .."j natural 
size. — After Hooker. 

foliage leaves. In some cases the large vascular bundles 
occupying the main ribs undergo changes similar to those de- 
scribed for the bundles of the stem (* 141), by which sec- 
ondary wood and bast are produced. 

175. Leaf fall. — One of the secondary changes of most 
importance is the preparation for the fall of the leaf. This is 
made by the formation of a layer of secondary meristem across 
the leaf base at or near the point where it joins the stem. 
The cells at this point, with the exception of those constitut- 
ing the vascular bundles, begin a series of divisions at right 
angles to the axis. A transverse plate of cells is thus formed, 
some of which cells may become transformed into cork, mak- 
ing a line of weakness ; or, without such alteration, the 
cells may round themselves off by loosening along a definite 
line, so that the leaf is held only by the steles. The access 



THE LEAVES. H r 

of water to this crevice, and its freezing, serve to rupture the 

remaining tissues, and thus allow the leaf to fall by its own 
weight, or to be torn off by the wind. 

The scar left by the fall of the leaf is protected either by 
the cork already produced, or by mere drying of the exposed 
tissues. The leaflets of compound leaves fall in like manner. 
Sometimes provision for the leaf fall is begun as early as June, 
as in the Kentucky coffee-tree. In other plants provision 
for leaf-fall is begun late in the season, and in some, such as 
the oaks, it is very imperfect, so that the leaves are finally 
wrenched off by winter storms, or pushed off in the spring by 
the developing buds beneath them. 



PART II: PHYSIOLOGY. 

CHAPTER XI. 

INTRODUCTION. 

176. Division of labor. — The study of the external form 
and internal structure of plants may be carried on as well 
upon dead as upon living material. Even the observation of 
the various stages of development requires only the examina- 
tion of the plant as it exists at a particular moment. But the 
plant may also be studied as a working organism. For this 
purpose living material is indispensable. The work which 
plants do and by which they are distinguished from non- 
living bodies is extremely varied, and the more complex the 
plant the more varied it is. In the preceding part the aim 
has been to show that there exists great variety of form, and 
that from the smaller to the larger plants there is gradually 
increasing complexity by differentiation into tissues and 
members. 

Nutrition, respiration, growth, movement, and reproduction 
are all executed by the single cell of the simplest plant. 
But with specialization in structure there occurs division of 
labor. Each kind of physiological work is known as a 
function, and each part of the organism which does a par- 
ticular work is called an organ. 

177. Physiology and ecology. — Physiology proper treats 
of the plant at work, discussing the different functions and 

M3 



144 PLANT LIFE. 

the way in which these are affected by external forces. In 
its broadest sense it also treats of the relation of the plant as 
a whole to external forces and to other living beings, both 
plants and animals. But it is convenient to separate the 
latter from physiology proper as ecology.* (See Part IV.) 

The study of physiology proper necessitates methods of 
controlling these external forces, carefully planned and re- 
peated experiments, and cautious inferences. 

The study of ecology requires observation in the field of 
the adaptations of plants to prevent injury by unfavorable 
physical conditions and the attacks of other beings, and to 
take advantage of the favorable forces and beneficent agents. 

178. Chemical and physical forces. — The functions of a 
plant may be divided for the sake of convenience into nu- 
trition, respiration, growth, movement, and reproduction. 
These are largely special modes of chemical and physical 
action. Nutrition and respiration, for example, consist 
chiefly of a series of chemical changes ; while movement is 
mainly a result of physical alterations in certain organs. 
But the action of chemical and physical forces does not suffice 
at present to explain all the phenomena of the living plant. 
Moreover, the peculiar manifestation of these forces which 
we call life occurs only in connection with the substance 
which we call protoplasm. 

179. The unit of function. — The functions performed by 
the entire plant are necessarily a sum of the functions per- 
formed by the physiological units of which it is composed. 
As the unit of structure is the plant cell, so the unit of 
function is the protoplasmic body of that cell. Although 
only a portion of any plant is composed of living matter, it 
is to that living matter only that we are to look for the seat 
of its powers. 

* Spelled in lexicons, cecology, but best usage drops the o ; sometimes 
improperly called biology or plant biology. 



INTRODUCTION. 145 

180. The fundamental powers of protoplasm arc tour ; it 
is metabolic, irritable, contractile, and reproductive. 

181. Metabolism. — Protoplasm is metabolic, thai is, it is 
capable of initiating a series of chemical changes in itself and 
in substances which come directly under its influence. These 
changes are of two kinds. They may be constructive, i.e., 
they may build up complex substances out of simpler ones, 
and so fit them for use in repairing the waste caused by the 
activity of the protoplasm; or they may be destructive, i.e., 
they may break down complex substances into simpler, so 
setting free the energy necessary for the work of the pro- 
toplasm. The substances broken down may be repaired in 
whole or in part, i.e., may take part in constructive me- 
tabolism. Those in which no repair occurs often undergo 
further destructive changes by which they become converted 
into materials useless to the plant, and to be gotten rid of. 
Metabolism, therefore, includes all the chemical changes by 
which food is either manufactured or utilized, and by which 
waste materials are produced and eliminated. 

182. Irritability. — Protoplasm is irritable, that is, it 
exists in such a state that it is sensitive to external influences, 
which thereby affect the various functions of the whole 
organism By reason of its irritability, it may even transmit 
the effects of an external stimulus from one part to a distant 
part. Moreover, it is capable of initiating similar changes 
without the action of any observable external influences, and 
is, therefore, not only irritable but automatic. 

183. Contractility. — Protoplasm is contractile, that is, it 
has the power of altering its form, of shortening in one 
direction and elongating in another, by virtue of inherent 
forces whose action is not understood. 

184. Reproduction. — Protoplasm is reproductive, that is, 
it is capable of so directing the chemical and physical forces 



I46 PLANT LIFE. 

inherent in it that a new organism similar to that of which it 
forms part may be produced. 

185. Adaptation.- -The interrelation of these powers, 
their harmonious coworking and their variation to suit the 
varying conditions of the surrounding media (air, water, soil, 
etc.), result in the proper performance of all the functions of 
the plant. By means of these powers it is brought into re- 
lation to the world about it, being adapted to other organisms 
in whose company it lives, and enabled to withstand the 
adverse conditions by which it is frequently threatened. 
Every organism, indeed, must adjust itself first to the external 
physical conditions, and, second, to other organisms. (See 
Part IV.) 

186. Physical conditions set limits upon the discharge of 
its functions. Varying amounts of light, of heat, of moisture, 
determine more or less rigidly how rapidly, or to what extent, 
each function may be discharged. Every function of the 
plant is adapted, therefore, to an upper limit, the maximum, 
and to a lower limit, the minimum, above or below which 
the performance of the function in question is impossible. 
Between these limits there lies some point at which it pro- 
ceeds most rapidly and effectively. This point is known as 
the optimum. 



CHAPTER XII. 

THE MAINTENANCE OF BODILY FORM. 

Every plant is capable of attaining and maintaining a 
specific form, which is not permanently altered by the direct 
action of external forces, and is dependent upon the nature 
of the plant itself. 

187. Naked cells. — If the plant consists of a single mass 
of naked protoplasm, it may assume a spherical or ovoid 
shape (fig. 1 68). In attaining this form the physical forces 




Fir.. iftS.— Zoospores of various Forms, 
cilia. ./, Botrydium ; />', Draf>ai 
Highly magnified .—After Kerner. 



vimming in water by means of one or mo 
aldia; ( ', Coieockate ; J>, CEdogoniui 



constituting surface tension play a part, but the form is deter 
mined chiefly by internal forces inherent in the protoplasm. 

This is particularly well shown when such organisms extend 
delicate protoplasmic threads, the cilia, and maintain these 

i47 



148 



PLANT LIFE. 



in active motion (fig. 168), or when they extend a portion of 
the body as a pseudopodium (fig. 169). 




FlG. 169. — Plasmodia, creeping bits of naked protoplasm, showing varied shapes 
parts are protruded or withdrawn. Highly magnified.- Artel Reiner. 



188. Turgor. — If the organism be one surrounded by a 
cell-wall, or if it be made up of a number of cells united, the 
cell-wall itself plays a considerable part in maintaining the 
form. This is due to the condition of the cell known as 
turgor. When fully mature the cell-wall of each active 
cell is lined by a more or less thick layer of living proto- 
plasm. In the interior of the protoplasm there exist one or 
more water chambers, the vacuoles (^[ 5). If such a cell as 
this be measured in its normal condition, and then surrounded 
for a few moments l>v a 10 per cent, solution of common salt, 
reexamination will show that the vacuoles have been dimin- 
ished, the protoplasm shrunken away from the wall, and 
remeasurement will show that the cell has diminished both in 
length and diameter. In its normal condition, therefore, the 
wall was stretched by the pressure of the contents within. If 
a cell which has been thus shrunken by immersion in a solu- 
tion of salt be again placed in water, it may regain, in the 
course of a few hours, its original condition, that is, it may 
again become turgid. This would be brought about by the 
entrance of water into the vacuoles to replace that withdrawn 
when the cell was placed in the solution of salt. 

If a thin piece of rubber tubing be connected with a pump 
and filled with water until it is stretched, it increases its 



THE MAINTENANCE OF BODILY FORM. M9 

diameter and length slightly, and gains, at the same time, a 
condition of rigidity greater than in its unstretched condi- 
tion. In a similar way turgid cells are more rigid than those 
which are flaccid. The union of turgid cells produces a 
member more rigid than one in which the cells are not turgid. 
An illustration of this is to be seen in the condition of a 
wilted, as compared with a fresh, leaf. The turgor of thin- 
walled cells may play an important part in maintaining the 
form and position of the parts of a plant. 

189. Tissue tensions. — But turgor can affect only those cells 
whose walls are thin and extensible. Those whose walls have 
become thick and rigid are not stretched by this force. In 
the larger plants, however, where both thick-walled and thin- 
walled tissues exist, it is possible that a mass of thin-walled 
cells may, by the united tension of its component cells, 
stretch those tissues which are not themselves turgid. Such 
strains in the younger regions, particularly, play an important 
role in maintaining the form of these parts. But the tensions 
in the older parts are generally due to the unequal growth of 
different tissues. (See ^| 259.) 

190. Mechanical rigidity. — The rigidity of the cell-wall 
itself must be relied upon by all the larger plants. Certain 
tissues are specialized by having their cell-walls greatly 
thickened, and such tissue regions constitute a sort of frame- 
work or skeleton, which is filled out by the more delicate 
tissues. These mechanical tissues are so distributed within 
the body as to afford frequently the maximum resistance to 
bending and breaking strains. In the accompanying dia- 
grams the position of the mechanical tissues is indicated in 
transverse sections of a number of different stems (fig. 170). 
It will be seen that they illustrate well-known mechanical 
principles in their distribution. The hollow column (E) and 
the [-beam (A, />', C), two of the most rigid mechanical con- 
structions, are frequently imitated in plants. 



ISO 



PLANT LIFE. 



In stems of trees rigidity is secured not by the distribution 
of the mechanical tissues, but by their massiveness. In them 
the chief mechanical tissues belong to the wood, which forms 




Fig. 170.— Diagrams showing the arrangement of mechanical tissues and vascular 
bundles in the cross-section of various stems. The mechanical tissue is gray; the 
vascular bundles black, with white dots. A, linden (young) ; B, a mint ; C, a sedge ; 
If, a bamboo ; A, a grass. — After Kerner. 



a solid column occupying the center of the body. Those 
plants which are supported by the medium in which they 
live, such as the aquatic plants, are usually without mechan- 
ical tissues. 



CHAPTER XIII. 

NUTRITION. 

191. Repair and growth. — Since the body of every plant 
is constantly wasting away by reason of its own activity, it is 
necessary that it should be as constantly repaired. It must 
also, for a considerable time or throughout its whole life, be 
furnished with material which can be used in the making of 
new parts. Without an adequate supply of food, therefore, 
neither repair nor growth is possible. To understand what 
materials are necessary for repairing waste and forming new 
parts of the living plant, the constituents of a plant may be 
determined by chemical analysis. 

192. Chemical composition. — The greater portion of the 
weight of every plant is found to be water. Of the firmer 
parts it forms as much as 50 per cent., while of the softer 
parts it may form 75 or even 90 per cent. The most watery 
portions of some plant bodies, such as the juicy portions of 
fruits and the whole body of the algae, may contain only 2 to 
5 per cent, of solid matter. The solid material, left after 
driving off the water at a temperature of no ('., is found to 
consist chiefly of three elements, carbon, hydrogen, and 
Oxygen. The most abundant element in addition to these is 
nitrogen. If the dry substance be burned these four elements 
are driven off in gaseous forms, and there remains a white 
material which crumbles under pressure, the ash. An analy- 
sis of the ash reveals the presence of sulfur and phosphorus 
in considerable amounts, and also smaller quantities of the 
following elements: calcium, magnesium, potassium, iron, 

151 



152 PLANT T.TFE. 

sodium, chlorine, and silicon. Of these seven, the first four 
are found in the ash of all plants, and the remaining three 
are very common. In addition to the elements enumerated, 
about 25 others are known to occur in the ash of plants, but 
only in minute quantities. 

A. The water in the plant. 

193. Necessity. — Since water forms such a large percent- 
age of the weight of fresh plants, it is manifest that it must be 
supplied in relatively large quantities, if the plant is to con- 
tinue in an active condition. A portion of this water may 
be used up in the chemical changes occurring in the body, 
but it is not possible to discriminate between this and the 
water which is necessary to furnish the proper physical con- 
ditions of life. Water is the great solvent by which materials 
of various kinds are carried into the plant body, and 1>\ 
which a still greater variety within it are transported from 
plaGe to place. Before discussing the food of plants, there- 
fore, the relation of water to the plant may be examined. 

194. Air, water, and land plants. — Some plants are not in 
contact with water except at irregular intervals. These are 
called air plants, and include some algae, liverworts, mosses, 
fernworts, and seed plants. All these, however, are able to 
live onlv in an atmosphere containing large quantities of 
water vapor, or in those regions where they are frequently 
sprayed with water. Water plants float upon the water, or 
arc submerged in it. As distinguished from both air and 
water plants, are those which normally have the mot system 
and sometimes a portion of the stem buried in the soil, con- 
tinually or intermittently in contact with liquid water, while 
the shoot system is occasionally sprayed by rain. Such may 
be called land plants. 

195. Solutions in water. — In no case, however, is the 
water in which plants are immersed, or with which they 



NUTRITION. 153 

are sprayed, pure water. It always holds in solution sub- 
stances derived from the atmosphere or from the soil with 
which it has come in contact. These substances are either 
organic or inorganic, and they enter the plant, along with 
the water, through those organs which are adapted to ab- 
sorption. 

196. Absorption of water. — In air plants of the simpler 
sorts, any parts exposed to the moist air or rain can absorb 
water. In liverworts and mosses the thallus or the leaves 
are active absorbents. In the higher plants, such as the 
aerial orchids, the external cortex of the roots is especially 
adapted to absorb liquid water, or to condense the water 
vapor of the atmosphere.* In water plants the surfaces which 
are normally in contact with the water are absorbing surfaces. 
Such plants may be either wholly without a root system, or it 
may be only sufficiently developed to anchor them in the 
mud. In land plants the root system is especially adapted to 
the absorption of water. Only minute quantities of water 
are absorbed by the leaves and other aerial parts. The re- 
vival of a wilted plant by spraying seems to be due more 
largely to checking the loss of water by evaporation than to 
the slight absorption which may occur. The root system of 
the land plants is developed in contact with the soil. 

197. Soil. — The soil consists primarily of finely divided 
particles of rock, whose nature and size determine the quali- 
ties by which soils are ordinarily distinguished into gravelly, 
sandy, loamy, clayey, etc. Mixed with these rock panicles 
is more or less organic material derived from the offal of 
plants or animals. When decaying plant offal predominates, 
the soil is known as vegetable mold or humus, which natu- 
rally forms the upper layer of the soil of forests. To garden 
or field soils, not naturally rich in organic matter, this is 

* If such condensation really occurs (as is generally alleged), it does 
not suffice to keep the plants supplied with the required amount of water. 



54 



rLANT LIFE. 



frequently added artificially. Both manure's and artificial 
fertilizers (the latter consisting usually of dried and ground 
animal offal) arc added chiefly for the purpose of supplying 
compounds of nitrogen and phosphorus. 

198. Soil water. — No matter how fine the soil may be, the 
rock particles are not in close contact, but, on account of 
their angular outline, leave spaces of greater or less size to be 
occupied by other materials. If a soil be examined immedi- 
ately after a heavy rain-fall, these spaces will be found com- 
pletely occupied by rain-water. If the soil be so situated as 




Fig. 171.— Diagram of a portion of soil penetrated by root hairs, h. A', arising from 
root, ''. At =, .f, ,v' (lie hair lias grown into contact with sonic of the soil particles, /. 
which are surrounded by water films (shaded by parallel lines), 0, o, t. The white 
spaces are air bubbles, S, &', y, y' . When water enters the hair .it a, the thickness of 
the film a, 3, t will be diminished, and some water will flow towards this point, re- 
ducing all the other water films in the vicinity. Move air enters from above. When 
rain falls, the reverse process occurs; the films thicken, and the air may be entirely 
driven out, to return as the surplus water drains away. After S.u lis. 

to be naturally drained, considerable quantities of this water 
will disappear gradually, and the larger spaces between the 
soil particles will be occupied partly by films of water adherent 
to the soil grains, and partly by bubbles of air (fig. 171). 

199. Salts dissolved. — The water which thus filters 
through the soil dissolves and retains certain of its constitu- 
ents. As the rain passes through the atmosphere it also dis- 



NUTRITIOX. 155 

solves certain substances found therein, notably minute quan- 
tities of ammonia and nitrous acid. By this means compounds 
containing nitrogen are constantly being brought to the soil 
by the rain. 

200. Root absorption. — The structure of the root system 
has been explained (% 78-82). The root hairs come into 
close contact with the soil particles, pushing them aside 
somewhat, and being in turn more or less deformed by their 
resistance (z, s, fig. 171). So close does the contact of the 
root hairs and soil grains become that many particles of the 
soil are imbedded in the walls of the root hairs (fig. 84). 
The root hairs are not only in contact with the soil particles, 
but also with the films of water, which occupy the spaces be- 
tween them (a, fig. 171). They are thus in a position for 
absorbing water from the adjacent films. 

201. Limit of absorption. — Not only is the water im- 
mediately in contact with the root a source of supply, but 
even that in the deeper and more distant parts of the soil. 
For when, by the entrance of some water into the root hair, 
the thickness of that layer has been decreased, the disturbance 
of equilibrium causes a flow from neighboring layers to 
equalize again the surface tensions. This goes on until the 
films of water upon the soil grains become so thin that the 
water particles are held too tenaciously to be pulled away by 
the root. There remains in such exhausted soil, which seems 
dry as dust to the touch, 2 to 1 2 per cent of water unavailable 
for the plant. 

202. Solvent action. — The root hairs also exert a slightly 
solvent action upon the soil particles themselves by reason of 
the carbonic acid and the acid salts which they excrete. By 
this means various minerals, especially carbonates of lime and 
magnesia (limestone), which could not be dissolved by the 
water alone, may be brought into solution. 

Water enters the root hairs by the physical process known 



156 PLANT LIFE. 

as osmosis, the protoplasm, braced by the cell-wall, acting as 
the membrane, and the cell sap of the vacuole as the denser 
fluid of the osmotic pair. (See Physics.) 

203. The development of the root system is related to 
the character of the soil and to the amount and distribution 
of water and organic matter within it. Branching of the 
root system is much more profuse in the moister parts of the 
soil, as well as in those which contain more organic matter. 

204. Movement of water within the plant. — Once the 
water has gained entrance to the plant, it must move to those 
parts where it is to be used — i.e., to all the organs of the 
plant, but especially to the leaves, since from these there is 
the largest loss of water by evaporation (^[ 209). From the 
root hairs the water passes inward through the cells of the 
cortex, and reaches the stele. The forces which determine 
this movement and its direction are not fully understood, 
though osmosis probably plays a chief part. They are com- 
prehended under the general phrase root pressure. 

205. Root pressure. — The action of root pressure may be 
demonstrated by severing a suitable stem close to the ground 
and observing the water which flows out, after a short time, 
from the cut end. Careful examination of the cut surface 
will show that the water oozes out chiefly from the woody 
parts of the stele. The force with which water is extruded 
may be measured by attaching to the stump, by means of a 
rubber tube, a manometer (fig. 172). In this way it may be 
ascertained that in woody plants, such as the birch, the 
pressure sometimes becomes equal to that of five or six 
atmospheres. 

206. Route to the leaves. — After entering the xylem 
bundles of the roots, the water is thence transferred along the 
stem in the same tissues, which are continuous with those of 
the root. Since the xylem bundles form an unbroken line to 
the most remote parts of the leaves, passing out in the ribs 



NUTRITION. 



157 



and forming the finer veins, the water may be distributed to 

every part of the plant body. Within 

the wood it travels chiefly in the cavities 

of the large ducts or vessels, when these 

are present, though the walls, also, are 

saturated with it, and permit a slower 

movement. These ducts, although of 

great relative length (some up to 1 m.), 

are not continuous tubes like the veins 

of an animal, nor are they filled with 

water. The water is broken into short 

columns by numerous gas-bubbles, and 

in ascending to any considerable height 

must traverse many cell-walls. 

207. Motive power. — The force by 
which water is raised in the larger plants 
remains yet to be ascertained. The 
water does not flow along the ducts in a 
continuous current, as the blood in the Fl m 
veins, propelled by a force behind, for 
root pressure is not adequate to push it to 
the height attained. On the contrary, 
during the times of most active evapo- 
ration from the leaves, i.e., when the 
greatest supply is needed, root pres- 
sure becomes almost or quite negative. 
Capillarity is also inadequate. The 
diameter of the largest ducts is too small 
and the friction of the water against 
their sides consequently too great to 
permit the movement, by this means, of ln,/ 
a sufficient amount of water to supply the evaporation. 
Moreover, the interruption of the water columns by gas- 
bubbles produces surface tensions which quite overcome that 




a T-tube, R, is attached by 
a piece of rubber tubing, 
v. The other openings are 
closed by rubber corks, k, 
through one of which 
jussr-- ,1 small glass tube, 
r, bent into two unequal 
legs, containing mercury. 
Through the upper should 
pass a short piece oi glass 
tubing drawn out to a line 
point, to be sealed off in a 
flame after A' is filled with 
water. At the beginning of 
the experiment the mercury 
is about at the same level 

in both legs. As water is 
ton ed from tin- stump into 
A' by toot pressure the mer- 
lin v rives in the .inn f' 
and falls correspondingly 
Alter SachS, 



158 PLANT LIFE. 

of capillarity. It has been found that the bubbles of gas 
here mentioned often exist under negative pressure, as shown 
by the fact that a stem cut under mercury allows the mercury 
to ascend for some distance within the vessels. This negative 
pressure of the gases is due to the evaporation of water from 
the leaves, and the most recent researches point to this as a 
very important or even the chief factor in lifting the water. 
That the movement is not a function of living cells is shown 
by experiments in which stems of plants have been subjected 
to poisonous agents, or heated for many hours to a degree 
sufficient to kill all the living cells, yet without materially 
affecting the supply of water. 

208. The loss of water. — Water is constantly evaporating 
from the whole surface of the plant exposed to the air. Since 
this loss is probably more or less modified by the vital activ- 
ity of the plant, it has received the special name, transpira- 
tion. 

f — I 209. Transpiration. — In the higher plants transpiration 
from the surface is reduced by the waterproofing of the epi- 
dermis, so that most of it takes place from the surfaces of 
internal cells into the intercellular spaces, wherever these 
exist. Since the intercellular spaces are connected with each 
other and also, through the stomata. with the outside air, 
water vapor is constantly passing off by diffusion. The leaves, 
affording the largest exposure, are especially organs of trans- 
piration. After they have become fully expanded no appre- 
ciable amount of water is lost directly from their surfaces. 
I 210. Amount and regulation. — The amount of transpira- 
/ tion, therefore, varies with the structure of the leaf rather 
/ J than with its area. The temperature, percentage of water 
* and movements of the air affect profoundly the rapidity of 
transpiration. Hence arises the need of regulation by the 
plant, to prevent excessive loss. The guard cells of the 
stomata are irritable, so that external conditions affect their 



NUTRITION. 1 59 

turgor, [f both arc turgid, they become curved away from 
each other so as to increase the size of the opening between 
them. If they are flaccid, the thick ridges along the inner 
face of each cell straighten them, and so close the orifice 
more or less completely (figs. 161, 162). The presence or' 
absence of hairs upon the leaves, the existence of stomala 
upon one or both surfaces, the sinking of the guard cells 
below the general leaf surface, the distribution of the stomat; 
the thickening of the leaves, their inrolling (fig. 357), or 
revolution (fig. 359), have a decided effect upon the rate of 
transpiration, and may be adapted to regulate it. (See 
1T434ff.) 

B. Foods in general. 

211. Foods. — In addition to an adequate supply of water, 
food is required. Materials consumed by plants as food are 
either organic or inorganic. Organic materials are those 
which have been produced in nature by the chemical changes 
occurring within living bodies. Inorganic materials are those 
formed in nature by chemical reactions not occurring in con- 
nection with a living body. A very few of the simplest plants 
(bacteria) have been grown by the use of inorganic materials 
alone; only the minutest quantities of such substances are 
utilized by most plants as food ; but large amounts are used 
by all green plants for the manufacture of organic foods. 

Organic foods are of three kinds, carbohydrates, fats, and 
proteids. 

212. Carbohydrates are substances consisting of carbon, 
hydrogen and oxygen, so proportioned that there are 6 
carbon molecules (or some multiple of 6) while the two latter 
elements are combined in the ratio of two parts of hydrogen 
to one of oxygen. Well-known examples are sugars and 
starch. 



l6o PLANT LIFE. 

213. Fats. — These arc likewise combinations of the same 
three elements, but in them the hydrogen and oxygen do not 
exist in the ratio of two to one, the oxygen being much less 
in proportion. Some are solid at ordinary temperatures, 
while others are fluid. They are combinations of free fatty 
acids and glycerin. Upon the addition of an alkali, the fatty 
acids combine with it to form soap and other compounds ot 
less amount while the glycerin is set free Commercial ex- 
amples of plant fats are olive oil, linseed oil, and cacao butter. 

214. Proteids are foods consisting of at least five and 
generally of six elements, namely, carbon, hydrogen, oxygen, 
nitrogen, sulfur, and (ordinarily) phosphorus. These elements 
are complexly combined in varying proportions. Proteids 
are generally recognizable by their property of coagulation 
upon the application of heat, acids, or other agents. Well- 
known examples are the proteids forming the "white of egg." 
Examples from the vegetable kingdom are less familiar. 

Proteids always, and either carbohydrates or fats, or both, 
must be available in order that a plant may be properly 
nourished. Green plants obtain their food chiefly by manu- 
facturing it out of inorganic materials taken into the plant 
body from without. They are the only organisms, so far as 
known, which have the power of building up organic material 
from inorganic. They are, therefore, the ultimate source of 
the food supply of the world. 

215. Metabolism. — After suitable foods become available 
to plants, whether by manufacture or by absorption ready- 
made, they suffer various chemical changes both before and 
after becoming a part of the body. The changes by which 
foods are manufactured and assimilated and those by which 
the products of waste are gotten rid of are all comprehended 
under the term metabolism. 



NUTRITION. l6l 

C. Nutrition of colorless plants. 

216. Colorless plants. — By tin's really inaccurate phrase 
are meant plants which do not possess chlorophyll, though 
some of them are highly colored by other pigments. 

The colorless plants among the thallophytes constitute two 
large groups, known as bacteria and fungi. Among the seed 
plants, also, are found some devoid of chlorophyll. 

Many plants possessing chlorophyll show to the eye other 
tints than green, when other pigments are present in such 
quantity as to mask the green. This is notably the case with 
the so-called "foliage plants," in which reds, yellows, pur- 
ples, and browns are common. (See also ^|*[ n, 40, 45.) 

Colorless plants necessarily live either upon the decomposi- 
tion products of dead organisms, or in company with living 
organisms. Those which live upon dead bodies, whether 
these have lost their form completely or not, are known as 
saprophytes. Those organisms which live in association one 
with another are called symbionts and their relation is known 
as symbiosis. (See Chap. XXIV.) Some symbionts are 
antagonistic and stand in the relation of parasite and host, 
the name parasite being applied to the organism which 
depends for its food upon the supporting organism, called the 
host. 

217. Saprophytes and parasites may be either obligate or 
facultative. < )bligate parasites or saprophytes are those which 
can exist only upon living or upon dead organisms, respec- 
tively. Facultative parasites or saprophytes are those which 
can pass a portion of their existence upon decaying or upon 
living organisms, respectively. They are not able, however, 
to complete their life cycle except upon their appropriate 
substratum. 

218. Saprophytes. — Saprophytic bacteria live immersed 
in solutions of organic material, or surrounded by films of 



1 62 PLANT LIFE. 

fluid on the surface or in the interior of the organic material 
upon which they flourish. Saprophytic fungi either form 
their mycelium upon the surface of the organic matter, or, 
more commonly, they penetrate it more or less extensively 
by a profusely branched system of submerged hyphae. A few 
saprophytic seed plants form at the base of the stem an en- 
larged, tuber dike mass from whose surface great numbers of 
profusely branched roots arise. These penetrate the decay- 
ing material in all directions, and act as absorbing organs. 
A few have abundantly branched underground stems and 
have no permanent roots. 

219. Digestion. — Saprophytes whose surfaces are sur- 
rounded by food solutions have only to absorb them. Some, 
however, have power to convert into material soluble in water 
the solid insoluble foods with which they are in contact. 
This is brought about either by a direct action of the proto- 
plasm of the living plant, or by means of enzymes (•([ 237) 
excreted by it. Such chemical changes, by means of which 
insoluble solid materials are transformed into soluble ones 
and are dissolved, are quite like those which occur in the di- 
gestive tract of the higher animals, and, therefore, may Im- 
properly termed digestion. 

220. Assimilation. — After the food is absorbed, it under- 
goes various changes, collectively known as assimilation, by 
which it is enabled to become part of the living material of 
the plant body.* 

221. Fermentation and putrefaction. — Some saprophytes 
produce changes in the material upon or in which they grow, 
other than those described above. The more important 
changes may be comprehended under the two terms fermen- 
tation and putrefaction. Between these there is no sharp 

* This is not to be confused with the manufacture of organic food by 
green plants, to which the term assimilation is inaptly applied by most 
writers. 



NUTRITION. 163 

line of demarcation. Popularly the term putrefaction is ap- 
plied to the changes in nitrogenous substances which are ac- 
companied by offensive odors. Fermentation is commonly 
applied to the chemical changes occurring in sugary solutions, 
such as fruits, expressed juices, infusions, etc. Many bacteria 
and a number of fungi, notably those known as yeasts, are 
capable of producing fermentation in such solutions. The 
chemical changes produced are more extensive than those 
required for obtaining food. Ordinary brewer's yeast, for 
example, utilizes about 5 per cent of the sugar present in the 
solution for food, but breaks up the remaining 95 per cent 
into carbon dioxide, alcohol, and some other less important 
by-products. In putrefaction the by-products are commonly 
offensive gases, among which hydrogen sulfid (H„S) predomi- 
nates. A'arious other materials may be formed, among which 
not infrequently are virulent poisons. These are well known 
in certain putrefactive changes of milk, meat, etc. 

222. Parasites obtain their food either by growing upon 
the surface of the host and thrusting into its interior absorb- 
ing organs ; or by growing wholly in the interior of the host, 
breaking out to its surface only to form reproductive bodies. 

Parasites may work little apparent harm, or they may bring 
about local disease and death of the host. Their mode of 
obtaining food is not essentially different from that of sapro- 
phytes. They either digest solid foods, or absorb liquid 
foods, prepared by the host for its own use. Among the 
green plants there are some partial parasites, sin h as the mis- 
tletoe, which seem to obtain from their hosts chiefly the 
water and salts which they have absorbed. These materials 
they themselves elaborate into food. (See further «j 465.) 

D. Nutrition of green plants. 

223. Raw materials. — In order that the green plants may 
be able to manufacture their food, they require certain raw 



164 PLANT LIFE. 

materials, which arc obtained from the medium by which 
they are surrounded. These substances are a weak watery 
solution of various mineral salts, and a gas, carbon dioxide. 

224. Salts absorbed. — Along with the water which is 
taken into the plant go various amounts of dissolved material, 
a considerable portion of which consists of mineral salts. 
When plants grow in humus, or in water or soils containing 
organic matter, a variable amount of carbon compounds 
suited for food may be dissolved by the water and be taken 
up by the plant. To this extent the plant will live as a sapro- 
phyte, and no doubt many field and garden plants have been 
bred to require this sort of life. Among the mineral salts 
the most important are the salts of calcium and magnesium, 
which are present in all soils, in greater or less quantity, 
usually in the form of nitrates, phosphates, and sulfates. 
Compounds of two other indispensable elements, namely, 
iron and potassium, are dissolved in soil waters. In the 
same way at least seven additional elements are obtained by 
plants. Besides these, other compounds to a considerable 
number, of no use in forming food, are taken in. Silicon, 
for example, which is found in the ash of almost all plants, is 
of no value either as a food, or for the manufacture of food, 
although it plays an important role in increasing the rigidity 
of certain plants, and in protecting others from injury. 

225. Selective action. — Compounds of these elements 
exist in the water in various, though small, amounts. But 
they are not taken into the plant in the same proportions as 
they exist in the water. For each substance presented to the 
plant there is a certain degree of concentration at which its 
solutions are absorbed with greater rapidity than at any other. 
Substances which are utilized by the plant and which, there- 
fore, disappear as such within it by having their chemical com- 
position altered or by being stored up in a different form 
and so removed from solution, will enter the plant contin- 



NUTRITION. 165 

uously so long as the supply outside exists. Substances ab- 
sorbed by the plant and not utilized accumulate, and their 
solutions soon attain the same degree of saturation within the 
plant as outside, when they cease to be absorbed. It is for 
this reason that two plants growing upon the same soil may 
contain very unequal quantities of any important material. 
Plants thus exert a sort of selective action, but this selection 
is dependent upon purely physical laws, and is not directly 
under the control of the plant. 

226. Carbon dioxide. — Carbon dioxide, as such, is not 
found in nature. It instantly combines with water to form 
a gas known as carbonic acid gas, and this is ordinarily 
meant when carbon dioxide is spoken of. This gas exists in 
small quantities in the atmosphere, rarely exceeding one part 
in twenty-five hundred, except in secluded spaces. The 
constant currents in the atmosphere make its distribution 
practically uniform. On account of its ready solubility, this 
gas also exists in abundance in soil waters and in the larger 
bodies of water constituting streams, lakes, or pools. In a 
soil containing carbon compounds it is constantly being pro- 
duced by decomposition. The water which passes through 
the soil therefore has a larger percentage of this gas than the 
air, sometimes containing as much as one per cent. 

227. Absorption. — Water plants readily absorb the dis- 
solved gas by such surfaces as are exposed to the water. 
Floating plants have opportunity to obtain it both from the 
water and from the atmosphere. Land plants, although 
their roots are surrounded by a comparatively concentrated 
solution of carbonic acid, do not take up appreciable quan- 
tities by these organs. On the contrary, the absorption of 
this gas seems to depend entirely upon those cells which 
contain chlorophyll. The Stomata, which allow the internal 
intercellular spaces free communication with the outside air, 
are important organs, not only in regulating transpiration, 



1 66 PLANT LIFE. 

but also in permitting the absorption of this gas. Its con- 
tinued absorption depends upon its continuous removal from 
the cell sap in the manufacture of carbohydrates. 

228. Anabolism. — By this term arc designated the con- 
structive processes of metabolism, by which complex sub- 
stances are produced from simple ones. These materials 
belong chiefly to two classes, {a) carbohydrates, (b) proteids. 

229. i. Carbohydrates. — The process by which carbo- 
hydrates are produced is called photosyntax. The conditions 
under which photosyntax occurs are three : (a) the presence 
of chlorophyll, (b) the action of light, and (c) the presence 
of potassium salts. 

230. (a) Chlorophyll. — Chlorophyll, as has been shown 
in Part I, sometimes colors the whole protoplasm of the cell, 
but is more commonly found only in certain special struc- 
tures, the chlorophyll bodies. The real work of forming the 
carbohydrate depends, therefore, upon the protoplasm of the 
chlorophyll body. The purpose of the chlorophyll is to 
absorb certain portions of the light which falls upon it. If 
the light which has been passed through a green leaf, or a 
solution of chlorophyll, be examined with a spectroscope, 
seven dark bands appear in place of certain of the colored 
rays, because these have been stopped by the chlorophyll 
(fig. 173). ( >ne absorption hand lies between the red and the 
orange ( 3-9 of scale, fig. 1 73), another in the orange ( 1 1-14), 
the third, faint, in the yellow (17-20), the fourth at the 
edge of the green (30—32), while the fifth (53-73), sixth 
(75-93), and seventh (94-100) bands occupy most of the 
blue and violet. These last three blend into one extremely 
broad band, except when the light passes through very small 
quantities of chlorophyll. 

231. (6) Light. — The light absorbed by the chlorophyll 
furnishes the energy necessary to carry on the work of taking 
apart the carbonic acid and rearranging the molecules into a 



NUTRITION. 



167 



more complex substance. This energy cannot be supplied 
by the plant itself. An external source of energy is therefore 
necessary. What this source is is unimportant, provided the 




Fig. 173. — The absorption spectrum of an alcoholic solution of chlorophyll. A beam 
of sunlight passed through a prism is broadened into a strip, called the spectrum, 
which shows different colors, according to the length of the light waves, the longest 
appearing red and the shortest violet. Some of the light waves are stopped by 
absorption, and at these places black lines appear (Fraunhofer lines), the more im- 
portant being those below the letters B, <-', etc. When the sunlight passes through an 



alcoholic solution it absorbs those parts of the light corresponding to the dark bands 

lade visible ' 

:he Fran 
or roughly by the colors. — After Kraus. 



I to VII. These absorption bands are made visible by spreading out the light ray into 
a spectrum. The bands are located by the Fraunhofer lines, or by the artificial scale, 



energy be sufficiently intense. The light of an electric arc 
serves the purpose as well as sunlight, if its intensity be 
equal. 

232. (c) Potassium salts. — These take no part in the 
composition of the food produced, and their exact role is not 
understood. It is well established, however, that their 
presence is essential to the formation of the carbohydrate. 

233. The product of photosyntax. — The steps in the 
process of the building of carbohydrates are not thoroughly 
known. Present indications are that the material first pro- 
duced by the rearrangement of the molecules of carbon, 
hydrogen, and oxygen, derived from the carl ionic acid, is a 
molecule of the simplest carbohydrate, formaldehyde. CI !..< >. 
Several of these are then built up (by condensation and 
polymerization) into one of the more complex carbohydrates, 
such as cane sugar. Starch is generally the first visible prod- 
uct and appears as minute granules in the interior of the 



1 68 PLANT LIFE. 

chlorophyll bodies, but is probably a transformation product 
from a sugar, to whi'ch it is closely akin (hemic ally. 

234. 2. Proteids. — The formation of proteids is even 
more obscure. Apparently at some point in the series of 
changes following the formation of formaldehyde, molecules 
of nitrogen are added to form an amid. Amids, especially 
asparagin, leucin, and tyrosin, are common in plants. They 
may also be produced by the use of carbon, hydrogen, and 
oxygen from complex carbohydrates by katabolism (* 238). 
They are soluble in water, crystallizable, and, hence, can be 
carried by osmosis from cell to cell. From these, by the 
addition of sulfur and phosphorus, proteids are formed, but 
neither the steps in the process nor its conditions are well 
understood. Apparently the formation of amids occurs in 
green tissues and under the influence of light. It is probable 
that even among the green plants the formation of proteids 
takes place in other parts than the green tissues, as it is 
certain that this occurs also among the colorless plants. The 
proteids which are built up from the amids are used directly 
in the repair of protoplasm. Since carbohydrates are neces- 
sary to the formation of proteids, and since they can be 
manufactured only by the green plants under the influence of 
light, it will be seen how essential these plants are for the 
world's food supply. 

E. Storage and translocation of food. 

235. Storage and transfer, -both in the colorless and 
green plants it is necessary that the foods made or absorbed 
should be transferred from one point to another where they 
are to be used. The larger the plant, the more important 
does this transfer become. In many plants, also, it is 
desirable that a supply of reserve food be stored for use when 
a supply is no longer available from the outside or by 
manufacture. 



NUTRITION. 



1 69 



236. Storage. — In the higher plants storage places are 
secured by the enlargement of roots, stems or leaves, to form 




Fig. 174.— Reserve starch. .-/. two cells of a potato, showing enclosed starch grains 
The other contents not shown. A', compound starcli grains from a grain of oats 
Three of the component granules of a large grain are shown separately. (', starch 
giains from a bean. All highly magnified.— After kerner. 

reservoirs. Similar specialization of parts of lower plants 
occurs. Carbohydrates are sometimes transformed into fats 
for storage purposes, but carbo- 
hydrate and proteid reserve food 
is usually solid. Reserve car- 
bohydrates usually occur in the 
form of starch, sugar, cellulose, 
gum, etc. Reserve proteids are 
usually in the form of aleurone 
grains. The starch is deposited in 
the form of large rounded or oval 
grains (sphere-crystals), which often 

. . . Fig. 175.— Aleurone (proteid) grains. 

shOW layers 0\ dillcivnt composition /. from seed oi peony. ■>. to,,,, 

the outer, /'. from the middle, c, 
and density (fig. I74). FatS OCCUr from the inner layers. //, from 

. seed of castor bean a, in alcohol ; 
in liquid form as droplets of van- b, after treatment with iodine solu- 
tion and alcohol. In both, f, elo- 

ous size, and are only rarely solid, boid; <■. crystalloid. Very highly 

magnified. — After Zimmermann. 

Aleurone grains are really vacuoles 

filled with reserve proteids. Some of the proteids often 




17° PLANT LIFE. 

crystallize | producing a crystalloid), and other materials are 
frequently present, which form the globoid (fig. 175). 

237. Intracellular digestion. — When solid foods, insol- 
uble in water, are to be moved from one part of the plant to 
another it must be done by altering them into soluble sub- 
stances. This is accomplished by means of enzymes of differ- 
ent kinds, adapted to effect the alteration of various foods. 
The most abundant enzyme is diastase, which has the power 
of altering starch into a sugar called maltose. Enzymes fitted 
to transform proteids are also found in considerable amounts. 
When the foods have thus been brought into a soluble condi- 
tion, they dissolve in the water present and move from one 
part of the plant to another, chiefly by osmosis. As any 
given material is used up in growth or repair, or is altered 
into another substance, a constant stream of molecules of 
this material moves toward the point at which it is disappear- 
ing. Thus from the food sources it is transferred to the 
reservoirs and stored in suitable form. Thence, when needed, 
it is redissolved after digestion and carried to the active parts 
which utilize it. 



F. Katabolism. 

238. Destructive changes. — Coincident with the processes 
which result in the formation of complex organic substance 
out of simpler ones are those which result in its destruction. 
The constructive processes are grouped under the term anab- 
n/i.xm, and the destructive ones are designated as katabolism. 
In the green plants the anabolic changes predominate (be- 
cause of extensive photosyntax), with the result that the plant 
accumulates organic matter ; while in colorless plants kata- 
bolic processes predominate, with the result that the plant 
increases in bulk, but only at the expense of organic materials 
previously existent. In all plants, however, both the con- 



NUTRITION. 17 l 

structive and destructive changes go on at the same time 
and without conflict. 

239. Respiration. — A series of katabolic changes is in- 
cluded under the term respiration. It is a familiar fact that 
the higher animals cannot live without a constant supply of 
oxygen and a corresponding excretion of carbon dioxide. 
This is not so generally known to be true of plants. It is, 
nevertheless, true that no plant can live without a constant 
supply of oxygen and a corresponding excretion of carbon 
dioxide. The processes by which oxygen is obtained and 
carbon dioxide excreted constitute respiration. 

240. Respiratory ratio. — The ratio between the amount 
of oxygen consumed and carbon dioxide produced varies 
somewhat with the age and condition of the plant, as well as 
with the circumstances under which respiration occurs. 
Ordinarily the volume of carbon dioxide produced is approx- 
imately equal to the volume of oxygen consumed, and the 

ratio may be expressed thus: -— — 1. 

241. Respiration and photosyntax. — In the green plants 
respiration is masked in daylight by photosyntax. When- 
ever the green parts are sufficiently illuminated, the carbon 
dioxide produced by their respiration is consumed in the 
formation of carbohydrates for food, lint when these parts 
are not adequately illuminated, the process of photosyntax 
is interrupted, and respiration can be studied. The parts 
of plants which are free from chlorophyll, such as young 
flowers, buds, embryos, and the like, and all the non-green 
plants, allow the respiratory changes to be demonstrated 
readily. 

242. Aeration. — The oxygen consumed comes from the 
atmosphere, or from the molecules of this gas dissolved in 
water. Certain plants are adapted to aerial respiration, while 
others are adapted to aquatic respiration, but in either case 



172 PLANT LIFE. 

the gas used is the same. In the smaller and simpler plants 
the protoplasm absorbs oxygen directly through the cell wall. 
In multicellular plants, however, especially when these be- 
come large and complex, only the superficial cells could do 
this. The internal cells are too far from the source of supply 
to allow an adequate amount of oxygen to reach them by 
osmosis through other cells. In large plants, therefore, 
intercellular spaces are provided, communicating with the 
external air, and through these oxygen diffuses. In the 
land plants the intercellular spaces are continued through the 
epidermis, in which, with the guard cells, they constitute 
the stomata (•[ 166). On the older parts of woody plants 
which have begun to form a periderm the stomata are replaced 
by lenticels, through which the internal intercellular spaces 
communicate with the outer air (^[ 140). In the absence of 
stomata or lenticels, however, the oxygen may pass through 
any part of the surface of the plant. In submerged water 
plants, very large intercellular spaces are formed (fig. 117), 
permitting the existence of an internal atmosphere of con- 
siderable amount, within whose limits gaseous exchanges may 
occur. Oxygen may reach these intercellular spaces from 
the water through the superficial cells. 

243. Intramolecular respiration. — While free oxygen is 
ordinarily utilized for respiration, all plants seem to be 
capable of obtaining their supply for a short time from the 
organic matter of the plant itself. Such respiration has there- 
fore been called intramolecular respiration. It can exist at 
most for a few hours without producing disease and, sooner 
or later, the death of the plant. It is precisely parallel to 
the similar method of respiration possible among cold-blooded 
animals. A few plants of the simpler sort, such as the 
bacteria, rely wholly upon combined oxygen for their respira- 
tory supply. Such plants have adapted themselves to grow 
in the absence of free oxygen, which, instead of facilitating 



NUTRITION. 1/3 

their life processes, really checks them. They are known as 
anaerobic plants. 

244. Excretion. — The carbon dioxide produced by res- 
piration, when not used for photosyntax, is gotten rid of by 
the reverse of the methods described for the absorption of 
oxygen. 

245. Release of energy. — The purpose of respiration is 
to set free energy required for growth and movement. While 
plants are capable of utilizing radiant energy of the sun for 
photosyntax, they must set free within their own bodies the 
energy requisite for putting in place particles of new material 
to form new parts, and for the execution of movements, 
whether internal, such as the streaming or rotation of the 
protoplasm, or mass movements, such as those of leaves and 
other members, or movements of locomotion, such as those 
of swarm pores and sperm cells. (See ^| 276 ff.) The re- 
quired energy is set free by the decomposition of organic 
matter. 

246. Loss of weight. — As a consequence there ensues a 
loss of weight. If a plant, such as a seedling abundantly 
supplied with reserve food, be compelled to develop in dark- 
ness, and so allowed to make no additional food, it may be 
easily demonstrated that a large part, often as much as one 
half, of its weight will be lost (as gases) in respiration. This 
loss of weight conies primarily from the decomposition of 
portions of the living protoplasm. These, however, are soon 
replaced by the formation of new protoplasm from the pro- 
teids, and these again are replaced, as already described, by 
the use of carbohydrates and nitrogenous compounds. Ulti- 
mately, therefore, respiration results in a diminution of the 
reserve food, especially of the carbohydrates. 

247. A vital function. — Respiration is a function of the 
protoplasm, and does not occur simply because oxidizable 
substances are present in the plant and oxygen is brought 



1^4 PLANT LIFE. 

into contact with them. On the contrary, the oxygen seems 
to enter into loose combination with protoplasm, forming 
an extremely unstable compound which under unknown con- 
ditions breaks down into simpler substances, setting free 
energy. Some of these materials are again used in building 
protoplasm, while others break down still further, ultimately 
into water and carbon dioxide. The supply of oxygen is so 
necessary that if a plant cannot obtain oxygen from without, 
it will secure it by the destruction of part of its own sub- 
stance for a time, as shown by intramolecular respiration. 

248. Heat. — While this decomposition of the protoplasm 
in ordinary respiration is not a true oxidation, it nevertheless 
results, as oxidation does, in the evolution of heat. The 
amount of heat produced is usually not great enough, and its 
loss too rapid, to make it readily perceptible. Anything 
which prevents the radiation of heat will make its measure- 
ment possible. The germination of large quantities of seeds 
or the blossoming of a number of flowers in a confined space 
may raise the temperature as much as 15 or 20 above that 
of the air. The heating of hay, grain, and similar substances, 
which have been stored when moist, is due partly to the 
respiratory activity of bacteria and fungi, which grow rapidly 
under these conditions. Fermentative changes, which also 
occur under the same conditions, add to the evolution of 
heat. 

249. Light. — A few plants also produce light. This light 
is like that seen when phosphorus is exposed to the air in 
darkness, or when the end of a match is lightly rubbed. 
Phosphorescence occurs only in some bacteria and fungi. 
When it is seen upon decaying meat, fish, or wood, it is 
because these organisms are present. It does not arise from 
the decaying substance itself. Several of the larger fungi, as 
certain toadstools, have a mycelium capable of emitting this 
phosphorescent light. 



NUTRITION. 1/5 

250. Contrast between respiration and photosyntax. — 
Since the processes of respiration and photosyntax in green 
plants are so frequently confused, a contrast is here drawn 
between them. 

Respiration. Photosyntax. 

Occurs in all living cells. Occurs only in green cells. 
Indifferent to or retarded by Requires light. 

light. 

Consumes organic matter. Produces organic matter. 

Produces carbon dioxide. Consumes carbon dioxide. 

Consumes oxygen. Produces oxygen. 

Sets free energy. Accumulates energy. 

251. Other katabolic changes. — Besides those constitut- 
ing respiration, a considerable number of other katabolic 
changes occurr, which are not so closely connected with 
the vital functions of the plant. They result in the produc- 
tion of substances which are of no further use in nutrition 
and only of incidental value for any purpose. Such sub- 
stances may be stored in some out of the way place, or in 
such parts as are transient, and by the loss of these parts the 
useless materials are gotten rid of J or they may be excreted 
directly. The waste materials are either nitrogenous or 
non-nitrogenous. 

252. Non-nitrogenous by-products. — Among the non- 
nitrogenous materials the most important are the carbon 
acids. su< h as oxalic, malic, etc., the tannins, the resins, the 
gums and the volatile oils. These substances are either by- 
products of photosyntax, or they arise in the course of the 
assimilation of foods. Oxalic acid is usually gotten rid of by 
being combined with lime to form calcic oxalate, which 
crystallizes either in the form of squarish crystals or as long 
needles, the form depending upon the amount of water of 



1 7 6 



PLANT LIFE. 



crystallization (fig. 176). The resins, usually dissolved in 
an oil, are generally exereted into special intercellular spaces 




Fig. 176. Crystals found in plants. I, calcium carbonate; II-V, calcium oxalate; 
II, octahedron with blunt ends; III, compound crystals from the nectary of a mallow; 
IV, ,i, /■, needle crystals (raphides) from leaf of fuchsia ; V, cell from the fruit-Mesh 
of a rose showing a crystal, k, embedded in an outgrowth of the cell-wall, . . All highly 
magnified. — After Behrens. 



(fig. 17 7)- 




Volatile oils are secreted by glandular hairs 
(c, fig. 113); or are formed 
in the epidermis itself, as in 
flowers ; or are produced in 
chambers near the surface, 
the cells which produce the 
oil being disorganized to 
form the cavity in which 

Fig. [77. — Transverse section of an inter- 
cellular receptacle for gum-resin from the the drops lie (fig. 17^)- 
fruit of fennel. The secretion has been 

dissolved out by alcohol. The shaded cells Other materials, SUCh !1S 
lining the tube are the secretory tissue. 
Moderately magnified.— After Tschirch. salts of lime, arc sometimes 

excreted upon the surface of the plant. From glands in 
the flower, nectar, which is a solution of sugar, is excreted 
(figs. 179, 180). The loss of this food is compensated for 
by its attractiveness for insects, which incidentally serve for 
the transfer of pollen from one flower to another. Caout- 



NUTRITION. 



177 



chouc and gutta-percha occur in the milky juice of certain 
plants. 

253. Nitrogenous by-products. — Among the nitrogenous 
waste materials the most important are the alkaloids, such as 




Fir.. 178.— Section through oil-receptacles in rind of orange, a, structure at the beginning 
of the disorganization of the oil-producing cells; />, final condition, with two drops of 
oil occupying the cavity. Moderately magnified. —After Tschirch. 





Fig 






Fig. 180. 

d surface of the cup, >/, 



Fig. 179. — A flower of the red currant cut in half. The rouglu 

secretes nectar. Magnified 5 diam.— After Kerner. 
In.. 180. I, ,1 petal from the flower ol a buttercup {Ranunculus acris), showing the 

nectary, n. Magnified 3 diam. II, diagram of a longitudinal section ol tin- same 

through the nectary //. The tissue lining the pouch of the petal, b, secretes the drop 

of nectar, /. Magnified 8 diam. After Behrens. 

quinine, morphine, strychnine, nicotine, etc., which occur in 
the seeds, bark, or leaves, and are gotten rid of when these 
are dropped. 






CHAPTER XIV. 

GROWTH. 

254. Definition. — The growth of plants is continued for 
a much longer time than that of animals. In most cases it 
is continued in some part throughout the existence of the 
plant. There are also changes in the form of certain parts, 
particularly of the lower plants, which must be distinguished 
from true growth. Growth is a permanent change of form 
accompanied usually by an increase in size. 

255. Formation of new parts. — Each new cell originates 
in the division of some previously existing cell by a partition- 
wall.* The two cells so formed grow until they attain the 
size of the parent cell, when one or both may continue to 
grow until they attain a permanent form; then growth ceases. 
Those cells which do not develop into permanent tissue, but 
retain their power of division, constitute a mass of tissue at 
the tip of each branch or root, the primary meristem (^[ 77, 
101). Permanent tissue which resumes active division is 
called secondary meristem (^[ 86, 134). It will be seen, 
therefore, that every cell of a plant has been at some time in 
an undeveloped or embryonal condition. 

256. Phases of cell development. — The characteristics of 
this embryonal condition are the nearly uniform and small 
size of the cells, the relatively large nuclei, and the absence 
or small size of the vacuoles (A, fig. 181). As the cells which 
are destined to become the permanent tissues grow older 

* To this there are only unimportant exceptions. 

17S 



GROWTH. 



179 



they pass gradually from the embryonal stage into a second 
phase of development, the stage of elongation. This stage is 
marked by the rapid Increase of the cells in size and a much 
less marked increase in the mass of protoplasm present. In 
order to maintain the turgor of the cells, there is a great in- 
crease in the volume of water, which accumulates in one or 





Fig. [81. — Cells from young and mature fruit of snowberry (Symthoricarpui), seen in 
section. ./, three young cells, very small, walls thin, inn lei relatively large, vacuoles 
very minute; />', two, somewhat older ; larger, walls thicker, nuclei smaller, vacuoles 



several. A and />' magnified 300 diam. C, a single cell, mature, magnified 
di.1111.. inie third as much as . / and A'.- vacuole single, very large. The volume ol 
< is more than 1500 times one of the cells in A . h , cell-wall ; p, protoplasm ; <<•, nu- 
cleus; kk, nucleolus; s, vacuole. — After l'rantl. 

more large vacuoles ((", fig. t8i ). If the organ in question 
has an elongated form, such as the stem or the root, growth of 
the cells takes place chiefly in the direction of its long axis, 
although an increase also occurs in the transverse directions. 
During this phase the tells may attain a hundred or even a 
thousand times their former volume. Growth in length can 



180 PLANT LIFE. 

be studied by direct observation with a microscope, but more 
< onveniently by magnify ing the growth by mechanical means, 
so as to observe the movements of a pointer over a scale. 
Such an instrument is an auxanometer. Those forms of it 
which secure a continuous record automatically are of the 



Fig. 182. — Golden's auxanometer. The instrument 1 onsists of two parts, a multiplying 
pulley and two recording rods turned by a clock. V thread from the plant passes 
through a bent glass ,U ' ,L ' ,llu ' makes one turn around the small pulley to which it is 
then f.isti-iu-d. Another thread makes one turn around large pulley and descends 
to carry a pointer which slides on two guide rods. Asthe plant grows the thread 
from it slackens and the pointer descends at a magnified rate by its own weight. Two 
glass rods, blackened in a smoky gas-flame, are rotated by a clock to whose hour 
spindle the frame carrying them is atta< hed. Vs thl \ pass the pointer a mark is made 
on the smoked sulfate. The distance id the suciessive marks shows the amount of 
growth as magnified. Permanent record may lie made by means of blue prints, using 
the rods (which are removable) as negatives.— After Arthur. 

most service (fig. 182). By imperceptible gradations these 

cells pass into the third and final stage of growth, which is 



GROWTH. 



i8i 



characterized by permanent and usually irregular thickenings 
of the wall (figs. 10, n, 52, 58). 

257. Grand period of growth. — The entire duration of 
growth of an organ is known as its grand period of growth. 
Corresponding precisely to the phases in cell development, 
there are three phases in the development of the organ as a 
whole. Its growth is at first very slow, increasing gradually, 
and then more rapidly, to a maximum, from which it falls 
rapidly, and then more gradually, until it ceases entirely. The 
earliest phase, the embryonal, results in so little elongation 
that it is scarcely possible to have it recorded by the auxanom- 
eter. The last phase, that of internal differentiation, is not 









2V 


I \ 


t v 


4 \ 


/ \ 


S IX 


/ V 


t S 


4 s^ 


L ^ 


^ s ^ 




4 8 13 16 80 



Fig. 183. — Curve representing the rate of growth of an internode >>f crown imperial tor 
each day during the grand period — in this rase _'*. days. The height ol each \ ertical line 
where it intersects the curve represents the total growth for the corresponding 24 
hours. The numbers indicate days. The maximum growth occurred on the 6th day. 
— After Sadis. 



marked by any elongation. The accompanying curve (fig. 
[83) therefore represents only the duration and course of the 
phase of elongation. 

258. Growing region.— The part of any one of the multi- 
cellular plants, which is growing in length, is limited. The 
elongating region of a root rarely exceeds a centimeter, and 
is often not more than one halt a centimeter in length. In 



182 



PLANT LIFE. 



stems, however, the elongating part may measure twentyoreven 

fifty centimeters, and in rare cases 
much more. Figure 184 shows a 
root, A, upon whose surface marks 
were made 1 111111. apart. Twenty- 
four hours later the root presents 
the appearance of B. Only the 
tissues in the first five spaces were 
capable of elongation. The others 
had passed into the third phase. 
The second and third millimeters 
grew most in length. The growing 
regions of stems may be deter- 
mined in the same way. 

259. Tension of tissues. — The 
different tissues in any organ usu- 
ally do not grow at an equal pace, 
and consequently certain tissues 
are under strain, while others are 
compressed. The curled and 
crinkled leaves or the curved cap- 
sules of mosses illustrate this in- 




marked with fine lines of Chinese equality. It maybe present, how- 

ink into 13 spaces of i millimeter l J J * 

each. /:, the same root, 24 hours ever without manifesting itSt'lf ill 

later, showing elongation only in ' ° 

terminal 5 millimeters The rate of external form. This general COn- 
growth is greatest m the 2d and 3d ° 
millimeters and slow in the ,s,,,h. ( 1J, K)U jg kllOWliaS 1 1 1 C /etlSlOfl of 
and i\\\. .Magnified 1 chain. —Alter 

Prank. 



/issues. If the rapidly growing 
flower-stalk of the dandelion or the leafstalk of rhubarb 
be carefully split lengthwise the parts will curve or even curl 
outward. Separating the inner and outer tissues of a young 
elder shoot and carefully measuring them shows that tin- 
inner tissues elongate and the outer actually shorten. The 
experiment, therefore, shows that the inner tissues really 
grew more rapidly than the outer, but were compressed in 



GROWTH. 183 

the uncut stem, while the outer ones were slightly stretched. 
The strains thus set up are spoken of as longitudinal tissue 
tensions. Similar tensions due to unequal transverse growth 
may be shown to exist. If a thin transverse slice from the 
fleshy leaf-stalk of the rhubarb be divided into equal parts by 
a longitudinal cut it will be found in a few moments that the 
halves can no longer be made to touch throughout the line of 
the cut, because it has become convex. Both the longitudi- 
nal. and transverse tensions may be exaggerated if the parts 
be placed for a few moments in water. 

260. Conditions of growth. — That plants may grow cer- 
tain conditions are prerequisite. (1) There must be an ade- 
quate supply of constructive materials. These may be derived 
either from food recently manufactured or from that stored 
in reservoirs, or, in the case of the colorless plants, from that 
absorbed from without. (2) There must be a supply 0/ oxy- 
gen for respiration. This is needed, as previously explained, 
to set free the energy necessary for growth. (3) There must 
be a supply of water adequate to maintain a minimum turgor 
of the cells, without which growth cannot take place. (4) 
A suitable temperature is required. The range of temperature 
within which growth may take place is extensive, and varies 
with the individual plant. In general, the upper limit may 
be stated as about 40 C, and the lower, about o° C. The 
minimum of plants of tropical regions is approximately io° C, 
while the maximum for plants of the arctic or alpine regions 
is much below 40 C. Between the maximum and minimum 
temperatures there is an optimum temperature for each plant, 
at which growth takes place most rapidly. For most plants 
the optimum lies between 25" and 32 ('. 

261. External conditions exercise a very important in- 
fluence upon the rate or character of growth by reason of the 
irritability of the protoplasm. (See further - 418.) Many 
of these conditions act upon members of the plant so as either 



1 84 PLANT LIFE, 

to bring about permanently unequal growth in a certain part, 
or to cause one part to grow more or less rapidly for a time 
than another. Such variations in growth produce curvatures 
in the parts concerned and move members connected with 
them. They are therefore discussed in the chapter on Move- 
ments. Those conditions which act more generally and 
uniformly upon a large number of plants have a tonic eflfei t 
and serve to determine the form and mode of development of 
members. 

262. Light. — The tonic effect of light is different upon 
different plants and even different members of the same plant. 




\ 



A 



Fig. 1S5. — Part of the transverse sections of the stem of rye. . I. From a plant grown 
fully exposed to light; /■'. from a "laid" plant imperfectly exposed to light, n , 
epidermis; b, c, mechanical tissues; </, thin-walled tissues. Highly magnified.— After 
Koch. 

In general light retards growth in length. Stems grown in 
darkness usually become excessively elongated. Those 
which under normal illumination have internodes very 



GROW TIL 



I8 5 



short, in diminished light may have them well developed, as 
occurs, for example, in dandelions growing in deep shade. 

In general, light accelerates the growth of leaves in area. 
Leaves of shoots grown in darkness remain small. 

Light affects not only the external form but the internal 
structure. In diminished light the cell walls do not thicken 
normally, and mechanical tissues are weakened. " Laying" 
of oats and such grasses is mainly due to this cause (fig. 185). 
In weak illumination the palisade tissue of the leaves (% 167) 
is poorly developed. 

263. Light and temperature. — The combined variation 
of light and temperature between day and night establishes a 
daily period in the growth of all plants. The withdrawal of 
light at night permits an increase in the rate of growth in 
length, which reaches its maximum in some plants shortly 
after midnight, in others not until the early morning. During 
the day its retarding effect diminishes the rate of growth, 
which reaches a minimum some time in the afternoon. The 




5 ; ■■) 11 1 3 5 7 y 11 1 s 5 7 a 11 1 

N M N 

Fir.. 186.— Curve showing the daily period in the growth of a stem of rye. The vertical 
lines represent 2-hour periods from 5 P.M. of one day to 5 a.m. of the second day. 
the shaded parts indicating the actual hours of darkness. The horizontal lines repre- 
sent tenths of a millimeter. The curve is drawn by taking the record from an aux- 
anometer and laying off on the vertical line For each interval the growth shown, The 
points arc then joined. It will be observed that the maximum rate ol growth 

shortly after the period ol darkness (5 A.W I and the minimum rate alter the period of 
most intense illumination (5 P.M.). During the experiment the thermometer varied 

from [8° to 22 C. — After Frank. 



minor fluctuations in temperature, as well as the generally 
higher temperature during the day and lower during the night, 



186 



PLANT LIFE. 



introduce variations in the rate of growth, which obscure, but 
do not counteract, the retarding influence of light. (See fig. 
186. ) This daily period is so impressed upon the constitu- 
tion of the plant that it maintains it for a considerable time 
even when kept in complete darkness. Stems of sunflower, 
after two weeks in complete darkness, still showed distinctly 
the daily period. A similar daily period is apparent in 
the tension of tissues which depends 
on growth. 

264. Moisture and oxygen. — The 
amount of moisture and oxygen pres- 
ent in the medium surrounding a 
plant profoundly affects its form. 
Amphibious plants, that is, those 
which are capable of growing either 
on land or in water, often show this 

Fig. 187. — a shoot of water in a striking way. When grown sub- 
crowfoot {Ranunculus , , . 
aquatuis). The lower leaves merged, the leaves are usually finely 

have developed under water . , 

and are branched into many divided, while the 

narrow divisions; the two 

upper leaves have developed allowed to develop 

in air and at maturity float 

on the surface of the water, broad blades Scarcely 

About half natural size. — 

After Frank. (fig- 187). 




same leaves, if 
in the air, have 
more than lobed 



265. Mechanical pressures or strains also exert an in- 
fluence upon the rate and mode of growth. Compression of 
tissues retards their growth; strains accelerate it. Thus, 
stems enclosed in plaster casts or ligatured grow more slowly 
in thickness. Tensile strains, such as those exerted by wind 
or weight, promote the development of mechanical tissues. 
Petioles, which would break under a strain of 700 gm., after 
enduring a pull of 500 gm. for five days, broke only at 1600 
gm. Alter five days more under a strain of 1200 gm. they 
could not be broken with less than a weight of 6500 gm. 

266. Variations in rate. — There are not only variations 
in growth in the course of each day throughout the growing 



growth. 187 

period, but also minor variations independent, so far as 
known, of external conditions, which are therefore called 
spontaneous variations. Irregular variations occur from hour 
to hour in the course of the day. Regular spontaneous 
variations, also, occur in various organs, particularly in the 
tendrils of climbing plants, and in the leaves of flowers and 
buds. These regular variations, which affect different sides 
of bilateral organs and different sectors of cylindrical ones, 
bring about a bending of the entire organ from one side 
to another. These curvatures produce nutation, and will 
be further described under movements. (See ^| 283.) 

267. Duration. — Even when the external conditions of 
growth are kept as uniform as possible, growth does not con- 
tinue for an indefinite time. Having passed through the 
phases above named, it ceases, no matter how favorable the 
external conditions. Yet some organs, even after growth 
has ceased, may resume it, provided they are affected by 
suitable stimuli. Thus, the leaf cells which have long since 
ceased to divide may resume the power of division in the 
neighborhood of a wound, and by division and the growth 
of new cells may form a callus covering the wound. The 
stimulus following fertilization also induces growth in parts 
adjacent to the egg, as is most strikingly shown in the 
formation of fruits of the seed plants. (See ^| 404, 409.) 



CHAPTER XV. 

THE MOVEMENTS OF PLANTS. 

268. Irritability. — Among the fundamental properties of 
protoplasm are irritability and automatism. We know practi- 
cally nothing of the nature of either of these properties, 
though upon them depend all the movements executed by 
plants. Automatism is the name given to the power in 
virtue of which protoplasm is able to initiate internal changes 
without the action of any external force. Irritability ex- 
presses the power of the protoplasm to respond or react to 
the influence of an external change. 

269. Stimuli. — The external change which brings about 
the reaction is known as a stimulus, and its application is 
called stimulation. External forces which may act as stimuli 
are light, heat, gravity, moisture, electricity, chemical sub- 
stances, etc. Most of these act constantly upon plants. In 
order that they may act as stimuli, therefore, a relatively 
sudden change in intensity or direction must occur. Some- 
times, however, a slow change will still produce a reaction. 
For example, the gradual withdrawal of light may cause 
movements of leaves. (See ^[ 297.) 

270. Conditions limiting irritability. — Protoplasm is ir- 
ritable only under certain conditions, which coincide in the 
main with those that promote the general well-being or life 
of the organism. The limits of temperature, moisture, and 
the supply of oxygen, which permit irritability, are much 
narrower than those which permit life. Thus, irritability 
may be lost when the conditions are unfavorable, though life 



THE MOVEMENTS OF PLANTS. 1 89 

may persist under such conditions for a long time. Irritabil- 
ity may also be lost through fatigue, as when, after repeated 
reaction, no response occurs to even a greatly increased 
stimulus. Upon the return of suitable conditions, or after 
sufficient rest, irritability may be regained. 

271. Reaction. — The response of the protoplasm to a 
stimulus is out of all proportion to the physical or chemical 
action of the stimulus itself. The action of the stimulus upon 
the irritable protoplasm may be roughly compared to the 
action of the trigger niton a primed and loaded gun. It 
sets free forces vastly in excess of those which it exerts. 

272. Reaction time. — The reaction does not follow in- 
stantly upon stimulation. The interval, which is known as 
the reaction time, is ordinarily much longer in plants than in 
the higher animals. In extreme cases no reaction may be 
manifest until several hours after stimulation. In other cases, 
however, as in the well-known sensitive plant, the move- 
ments of the leaves follow almost instantly upon stimulation. 

273. Form of reaction. — The character of the reaction is 
not dependent upon the nature of the stimulus, but upon the 
nature of the organ itself. It is not in the least understood 
what the inherent peculiarities are which determine the form 
of the reaction. In different organs exactly opposite effects 
may be produced by the same stimulus, and the same organ 
at different ages may respond differently to the same stimulus. 
Thus the young internodes of the Virginia creeper {Ampe- 
lopsis) are sharply recurved, but become erect when older. 
The stalk bearing the flower of the peanut is erect, but as it 
becomes older it becomes strongly retlexed, and thrusts the 
fruit under ground. 

274. Localization of irritability. — In multicellular plants 
irritability to certain stimuli is usually localized in certain 
organs, and often in special parts of these organs. In many 
tendrils, for example, the free end is curved and only the 



190 PLANT LIFE. 

concave side is irritable to contact. In the Venus' fly-trap, 
although the whole leaf moves at the contact, only the three 
hairs upon the upper face of each lobe are sensitive to a 
touch. (See figs. 386, 205.) 

275. Transmission of stimuli. — In these cases, as in many 
others, the effect of the stimulus must be transmitted in some 
way from the point of application to the cells which produce 
movement. Much uncertainty exists as to how this is ac- 
complished. In some cases it is doubtless done by means of 
the connecting threads of the protoplasm from cell to cell, 
after the analogy of a diffuse nerve. In other cases it may 
be transmitted through certain strands of tissue by the altera- 
tion of the hydrostatic pressure in the interior of the cells. 

The movements of plants may be conveniently considered 
as (1) movements of locomotion by single cells; (2) move- 
ments of protoplasm within a cell-wall; or (3) mass move- 
ments of multicellular members of the higher plants. 

I. Locomotion of single cells. 

276. Naked cells. — Plants which consist of a single cell 
may be either naked or furnished with a cell wall. If naked, 
they may exhibit either amoeboid or ciliary movements. Amoe- 
boid movements are slow creeping movements brought about 
by the protrusion of a portion of the protoplasm (a pseudo- 
podium), toward which the remainder gradually flows (fig. 
169). Ciliary movements are due to the extension of one or 
more very slender threads, called cilia, whose rapid bending 
in different directions propels the organism (fig. 168). 
According to the nature of the movements, the course will 
be zigzag or steady, accompanied by the rotation of the cell 
on its axis. When the cell comes to rest the cilia are either 
withdrawn or drop off. 

277. Cells with a wall. — Movements of locomotion in 
plants possessed of a cell wall are either ciliary or creeping. 



THE MOVEMENTS OF PLANTS. 



1QI 



The latter are usually due to the protrusion of processes from 
the protoplasm through slits in the wall, as in many diatoms 
(fig. 20). The filaments of the water slimes bend from side 
to side, and so creep over wet surfaces very slowly (fig. 15). 
Bacteria (fig. 17) and some diatoms move by means of cilia. 



V) 

A 1 



II. Movement of protoplasm within a wall. 

278. Streaming. — In multicellular organs it is common 
to find the protoplasm within each active cell 
moving about from point to point within the 
cell. The protoplasm is filled with numerous 
large vacuoles, so that it forms a layer next the 
wall, with threads or ribbons extending across 
it (fig. 188). When currents start along the 
wall and through the strands, the motion is 
designated as the streaming of the protoplasm. 
These currents along any particular portion of 
the protoplasm may run side by side and in 
opposite directions. 

279. Rotation. — When the protoplasm sur- 
rounds a single large vacuole and thus occupies 
only the periphery of the cell (fig. 181, C), 
the whole mass may rotate, usually in the direc- 
tion of its long axis. The portion immediately 
in contact with the wall is motionless, and there 
must necessarily be a strip between the half Fie 
moving up and the half moving down the 
cell, which is also quiet. Such movements are 
called rotation of the protoplasm. It is not 
known whether either streaming or rotation 
has any immediate relation to the well-being 
of the cell. 

280. Cell organs. — In addition to the mass 
movements of the protoplasm, the smaller protoplasmic bodies 



A single 
cell from a hair of 
Chelidonium. 
The arrows show 
the direction of 
movement oi the 
protoplasm in the 
peripheral I a y e r 
and in the bands 
which separate the 
vacuoles, n, the 
nucleus, with nu- 
cleolus. Highly 
magnified. — After 
I lippel. 



192 PLANT LIFE. 

within the cell, such as the nucleus and the chloroplasts, are 
capable of moving about. Under moderate illumination 
chloroplasts accumulate upon the sides of the cells most di- 
rectly reached by the light. Under very strong illumination 
they retreat to the walls least illuminated, or may even pile 
up in the angles of the cell so as to shade each other (fig. 
189). 




&At 



Fig. 189. — Cells from the spongy parenchyma of the leaf fo wood sorrel {Oxalis), seen 
from the direction in which light falls on the leaf, a, position of the chloroplasts in 
diffuse light ; /', position after short exposure to direct sunlight ; c, position after longer 
exposure. Highly magnified. — Alter Staid. 



III. Movements of multicellular members. 

281. Forces. — The movements of multicellular parts may 
be brought about either by special organs known as motor 
organs, or by the growth of the immature parts. Motor or- 
gans are generally responsible for the movements of mature 
[tarts, while movements of the younger regions are generally 
due to growth. The force exerted by the motor organs is 
dependent upon the altered turgor of the cells of which the 
organ is composed. If the cells upon one side lose their tur- 
gidity, those upon the other, being unresisted, will extend 
and bend the organ toward the side upon which the turgor 
was diminished. It will be convenient, therefore, to dis- 
tinguish movements due to growth and movements due to 
variation in turgor. 

282. (A) Movements of growth. — These depend upon 
some inequality in the rate of growth of the organ concerned. 
They are of two sorts: (1) those in which variation ingrowth 



THE MOVEMENTS OF PL, IX VS. I93 

is produced by internal causes, called spontaneous move- 
ments, and (2) those in which the variation in growth results 
from stimulation by external agents, called paratonic move- 
ments. 

283. 1. Spontaneous movements. — Among spontaneous 
movements are those in which the variation in growth occurs 
upon different sides of a cylindrical organ, or the two faces of 
a bilateral one. The opening of all flower and leaf buds illus- 
trates this movement, which is called nutation. During the 
development of the interior parts, the outer leaves (often 
scale-like) which protect them grow more rapidly upon their 
outer (dorsal) surfaces. They are thus pressed together into 
a compact bud. When the internal parts are suitably de- 
veloped a change occurs in the rate of growth of the outer 
leaves ; their inner (ventral) faces now grow more rapidly 
and the bud expands. Similar spontaneous variation in the 
growth of different sides of tendrils produces a nodding or 
waving motion, or even a rotation of the tip, by means of 
which they are often enabled to reach a support. In most 
tendrils the acceleration of growth travels irregularly around 
the axis, so that their tips rotate in a roughly circular or 
elliptical orbit from the time the tendril is two-thirds grown 
until growth ceases. The further changes in the tendril, by 
which it wraps the tip about the support and coils the re- 
mainder into a double spiral, are paratonic movements in- 
duced by contact. The rotating movements by which twin- 
ing plants climb are also paratonic and not spontaneous. 

284. 2. Paratonic movements are also of the highest im- 
portance for the well-being of the plants concerned. By means 
of them the different organs are developed in such situations 
that they can properly perform their work. The stimuli 
which influence the rate of growth are chiefly light, gravity, 
heat, mechanical contact, and moisture. The peculiar states 
in which a plant or an organ exists when it can respond to 



'94 



PLANT LIFE. 



the different stimuli have received different names, and those 
names indicate the nature of the stimulus. A plant or an 
organ is heliotropic when it reacts to the direction of the 
rays of light falling upon it ; geo/ropic, when it reacts to the 
force of gravity ; thermotropic, when it reacts to the presence 
of a warm body ; hydrotropic, when it reacts to the presence 
of a moist surface, etc. In each case the plants are said to 
react positively when the movement is toward the source of 
the stimulus ; negatively, when the movement is away from 
the stimulus ; transversely, when it is transverse to the direc- 
tion of the stimulus. These reactions are to a certain extent 




ODD 



Fig. 190. — Diagrams representing the transverse heliotropism of leaves of the garden 
nasturtium (Tropaolum). Potted plants were subjected successively to light strik- 
ing them in the direction shown by arrows. The petioles curved so .is to place the 
blades at right angles to the incident light. — After VSchting. 

related to one another, and it will be convenient, therefore, to 
consider the effect of each stimulus upon the two common 
forms of plant organs — namely, the radial (such as stems and 
roots) and the dorsiventral (such as leaves). Organs are 
sometimes physiologically dorsiventral, even though they 
possess a radial structure ; for example, some steins behave as 
dorsiventral organs, although they are perfectly radial in 
structure. 

285. (a) Heliotropism. — Heliotropism is the state of a plant 
or organ when it is irritable to the direction of light rays. 



THE MOVEMENTS OF PLANTS. 



195 



Light thus plays an important part in determining the position 

of organs. As a rule radial organs are either positively heli- 
otropic, as the stems and leaf-stalks, or negatively heliotropic, 
as the roots. Dorsiventral organs, such as leaves, are all 
transversely heliotropic, assuming a position at right angles 
to the incident rays, which is the most favorable position 
possible for the manufacture of food by the green parts (fig. 
190). Intense light, however, may bring about a different 
reaction, so that the leaves set themselves edgewise to the 




Fir,. 191. — Leaf mosaic formed by a horizontal shoot of Norway maple. The lengthen- 
ing of the petioles of individual leaves to avoid shading of the blade is marked. 
About one-third natural size. — After Kerner. 



direction of the rays. A fixed light position is usually 
reached by leaves by the time they become mature, and this 
is generally at right angles to the source of greatest light 
branches of trees show the leaves so arranged as to size and 
position that they shade each other as little as possible, form- 
ing the so-called leaf mosaics (figs. 191 to 193). The leaves 
of window plants also exhibit these movements very strikingly, 



196 



PLANT LIFE. 



because usually illuminated from one side. Plants kept in 
darkness have their leaves irregularly placed. 

286. (3) Combined movements due to variations in the 




Fig. hi2. — A shoot of thorn-apple or " jimson " weed, showing imperfect leaf mosaics 

of tall plants formed upon the same plan as in rosettes (fig. 193). One-seventh natural 
size. — After kerner. 

amount of light or heat or both are especially exhibited by flow- 
ers, whose opening and closing are frequently determined 




mw'^M 



V 

Fin. 193. — A rosette of leaves ol .1 bellflower (Campanula pusilla), showing lun^tli- 

ening of petioles of lower leaves so as to tarry blades from under upper leaves — 
After Kerner. 

thereby. With some plants the predominant stimulus is heat; 
with others, light. Closed flowers of the tulip or crocus may 
be made to open in 2 to 4 minutes by raising the temperature 



THE MOVEMENTS OF TLA NTS. 1 97 

15 to 20 . The flowers of the white water-lily (Nymphaea) 
and of the dandelion open in sunlight and (lose in shade. 
By marking upon their leaves a series of equidistant parallel 
lines with Chinese ink, and subsequently measuring the dis- 
tances to which they have been spread, all such movements 
can be clearly shown to be due to accelerated growth of the 
outer or inner surfaces, respectively. The protection of the 
flower parts or the proper discharge of the functions is secured 
by these movements, which must not be confounded with 
those due to the direction of light or heat rays. 

'287. (c) Geotropism. — Geotropism is the state of a plant 
or an organ when it is irritable to the action of gravity. 
Since gravity is exerted always in the same direction, it is 
plain that reactions to this force cannot be studied, as in the 
case of light, by altering the absolute direction in which 
gravity acts, but only by so changing the position of the 
plant that the force acts in a relatively different direction. 
The reaction to this stimulus and the fixed gravity position 
must not be confused with the simple effect produced by the 
weight of the parts concerned. Such effects are to be seen 
in the downward bending of some plants with slender 
branches, or the curvature of the flower or fruit stalks by the 
weight of the parts. True geotropic curvatures are brought 
about by acceleration of the growth of the irritable cells, 
and the curvatures produced may even be contrary to the 
direction of the force. If seedlings be grown in boxes upon 
the rim of a wheel rotating slowly in a vertical plane, so that 
they are successively subjected to the action of gravity in 
relatively different directions, it will be seen that while their 
members grow in nearly straight lines, the direction assumed 
by the stems and roots is quite as frequently abnormal as 
normal, because the effect of gravity which normally deter- 
mines the direction of growth of these axes is neutralized, 
since it now acts upon them from a new direction at each 



190 PLANT LIFE. 

successive moment (fig. 194). If the wheel upon which 
such seedlings are grown be rotated at a high speed, the cen- 




Fig. 194. — Seedling mustard plants grown on a cube of peat, T, attached to the slowly 
rotating axle, A, ./. of a <linnst.it. The direction of growth of roots and steins is 
controlled 
eliminated. 



:arness of moist surfaces, the action of gravity and light being 
ariable direction of roots and stems. At m and /'/.j aerial 



hyphaj of a mold have taken direction as far from the repellant moist surfaces as pos- 
sible. One half natural size. — After Sachs. 



trifugal force will become a constant one, and, acting in 
place of the neutralized force of gravitation, will determine 
the direction which the stems and roots will assume. Since 
the primary stems of most plants are negatively geotropic, 
when grown under such conditions they will turn toward the 
center of the wheel, while the positively geotropic roots grow 
toward the rim. Similarly, if the wheel be rotated rapidly 
in a horizontal plane the stem will be controlled by a com- 
bination of the force of gravity and the centrifugal force (the 
latter predominating if the speed is great), and will grow in- 
ward and upward, while the roots will grow downward and 
outward (fig. 195). 

288. Transverse geotropism. — Not all stems, however, 
are negatively geotropic, nor all roots positively geotropic. 



THE MOVEMENTS OF PLANTS. 



I99 



The central axis of both root and stem in the majority of 
plants is so, but lateral branches of both place themselves at 
an angle to the action of gravity, sometimes at a right angle, 
at other times at a highly obtuse or acute angle. That is, 
they are more or less perfectly transversely geotropic. What- 




Fig. 195. — Part of centrifuge, a, the axle, rotated at a high speed by water or electric 
motor, to which is attached the circular metal plate, r, r, carrying a disk of cork, A-. 
To the latter are attached two seedling beans, .(, B, by means of pins; rf, the primary 
stem; k, the primary root. Over the seedlings the cover, g, is placed to keep them 
moist. After a few hours the lateral roots have turned into the direction of the cen- 
trifugal force, which was sufficiently powerful to overcome that of gravity except near 
axis of rotation, .r. One half natural size. — After Sachs. 



ever the normal position of any organ, it will be regained by 
the growing parts as rapidly as possible when the plant is 
forcibly displaced. This can only be brought about by the 
curvatures produced by unequal growth of the younger parts. 

If a potted plant be laid upon its side for a short time and 
then erected before any response to the stimulus occurs its 
growing parts still curve to one side, although not so far as if 
they had been allowed to remain in the horizontal position. 

289. Grasses. — In only a few cases do the maturer parts 
of plants regain their power of growth under the stimulus of 
gravity. The basal portion of the intcrnodes of grasses, 
however, remain for a long time capable of growth ; hence, 



200 



PI.AXT LIFE. 



when grasses are Mown down or trampled their stems erect 
themselves by the geotropism of this basal growing zone 
(fig. 196). 




Vu.. 196. — Part of a wheat-stalk, showing strong geotropic curvature. The shoot was 
placed horizontal, and the growth of the basal part of the internode with the leaf-sheath 
connected with it was stimulated on the under side, the upper remaining short. No 
curvature occurs in the older part of the internode. About two thirds natural size. 
—After Pfeffe:-. 




Fig 



io. 107.— Root-cage, < in the lower edge of a sheet ol zim .1 little larger than the panes 
of glass selected is formed a water-tight trough oi the same material. Two panes of 
glass of suitable size are clamped together, with a piece of wood i cm. thick on three 
edges to keep them separate. Seeds are sown in fine soil evenly packed between the 
panes: these are set with the lower edge in the water-trough and a sheet of zinc is 
used to keep out light. The cage should be slightly inclined, as shown, so as to keep 
roots against the glass 1 rom 1 drawing by J. C. Arthur. 



THE MOVEMENTS OF PLANTS. 



20 1 



290. Root-cage. — Experiments upon the response of root- 
lets to the stimulus of gravity upon altering their position 
may be carried on by means of a root-cage, shown in figure 
197. It consists essentially of two panes of glass placed close 
together, between which, in finely sifted soil, the rootlets are 
grown. By inclining this root- 
cage at various angles it may be 
shown that not only the primary 
root, but its branches, strive to 
regain their normal angle with 
the direction of gravity. This 
is illustrated in figure 198, in 
which the dark portion of the 
rootlets represents the growing 
parts while the cage was in- 
verted. They then took about 
the same angle with the horizon 
as when in normal position. 

Many dorsiventral organs, 




system of a broad 
own in a root-cage, first in the 



in the normal position. The arrow 



aga 

sshc 



Slich as leaves, are transversely the direction in which gravity acted 

the different positions. The black por- 

geOtropiC, JUSt as leaves are tion of the roots were the parts growing 

. during inversion. Two thirds natural 

transversely hebotropic size.— After Sachs. 

291. Twining plants. — The movements of twining plants 
are due to a peculiar reaction to gravity. As the upper inter- 
nodes of a seedling elongate they soon become too weak to 
support themselves and bend over, becoming nearly horizon- 
tal. When this occurs the growth of the right or left flank 
of the stem near the bend is accelerated (whence the stem is 
said to be laterally geotropic). The horizontal part is thus 
swung around, twisting the stem and bringing a new Hank 
under the influence of the stimulus. If in its continued rota- 
tion the stem comes in contact with a nearly ere< t support 
the free part continues to rotate, growing longer at the same 
time, and encircles the support. The part below the point 



PLANT LIFE. 






Fig. 199.- 



a bit of the stem of the - 



of contact now becomes negatively geotropic, and its growth 
on all sides is equally accel- 
erated. The coils are thereby 
straightened until the stem 
clasps the support very closely, 
from which it is often prevented 
from slipping by angles or out- 
growths of various kinds, which 
roughen the surface (fig. 199). 

While gravity thus plays a 
large part in determining the 

(-^?H\ 'fffl'''ll^ position of both aerial and sub- 

'^""i Tpfoj^'f terranean organs, it must be 

remembered that it works con- 
jointly with many other stimuli, 
hop, .'showing the six angles, each The position of the members 

carrying a row ot emergences, crowned 1 

by a branched rigid hair with very sharp jg therefore, a resultant of the 

points. Magnified 3 diam. />, three 

emergences more highly magnified.- reactions to the various external 

After Kemer. 

forces which stimulate it. 
292. ((/) Hydrotropism. — Hydrotropism is the state of a 
plant or an organ when it is irritable to moisture. Hydro- 
tropic organs may bend toward or away from a moist surface. 
Roots are particularly sensitive to the presence of moisture. 
If a cylinder of wire gauze be filled with damp sawdust and a 
number of seeds planted near its surfa< e they germinate and 
the roots start to grow in the normal direction — i. e., directly 
downward. If now the cylinder be suspended at an angle, 
as shown in figure 200, the roots which pass into the air, 
stimulated by the moisture, curve toward the damp sawdust. 
Upon entering it the stimulus ceases, and they start again to 
grow downward, being positively geotropic. Again the 
Stimulus of the moist surface overcomes that of gravity, and 
they turn back to it, often threading themselves in and out 



THE MOVEMENTS OF PLANTS. 203 

of the wire gauze. Since only one-sided action of a stimulus 
determines direction of movement, if the air be saturated 
they continue to react to the stimulus of gravity alone. 

293. (t) Movements due to contact. — Contact, either 
gentle or forcible, and friction act as stimuli to modify the 
growth of many plant parts. Only rarely is the main axis of a 
plant sensitive to mechanical stimuli, except, perhaps, to long 
J 




Fir,. 200. — Apparatus for demonstrating hydrotropism. <i. a, a zinc disk, with hooks 
to which is attached a cylinder or trough of wire netting filled with damp sawdust. In 
this are planted peas, g; whose routs, li, i. k, m, first descend into the air but soon turn 
toward the damp sawdust again, m lias threaded itself in and out of the netting. — 
After Sachs. 

continued contact (or pressure) in the case of some twining 
plants. But in many plants lateral axes in the form of ten- 
drils (*^\ 115, 158) and leaf-stalks (^j 157) are irritable to 
contact, even to a degree far surpassing that of our nerves of 
touch. 

If the tip of a tendril (•[ 266), while still capable of growth, 
come in contact with a solid body, it will quickly become 
concave on the side touched, and thus will wrap about the 
object, if it be of suitable size. This curvature is due first to 
the shortening of the cells upon the concave side and later 
to unequal growth on opposite sides. Finally this effect 



204 PLANT LIFE. 

extends to all parts of the tendril, which begins to curve. 
As both ends are fast, it is a mechanical necessity that the 
curves become spiral coils, both right- and left-handed, ac- 
companied by a twisting of the tendril on its axis ( fig. 107). 
After the coils are formed the tissues of the tendril become 
thick-walled and rigid, so that the plant is attached to the 
support by a series of spiral springs. 

Other tendrils do not nutate, but are negatively heliotropic, 
and by contact their tips are stimulated to develop disks 
which apply themselves closely to the support, and send into 
its irregularities short outgrowths from the surface cells. 
Such plants are adapted to support themselves by walls, tree- 
trunks, etc. The Japanese ivy and one form of the Virginia 
creeper are notable examples. 

The coiling of the leaf-stalks is not unlike the first curva- 
tures described for tendrils (fig. 154). 

294. (B) Movements of turgor.— The movements just 
described are confined to members which are growing either 
throughout or in some part. As turgor can affect only tis- 
sues whose cell-walls are elastic (*j 188), the movements 
produced directly by variation in turgor can occur in such 
mature members only as are provided with special motor 
organs. In almost all cases these are leaves. Stimuli which 
regulate growth (^[ 284) may also affect motor organs, pro- 
ducing like curvatures. But elongation of any part of a motor 
organ by increased turgor is reversible, not permanent, (cf. 

II 254)- 

295. Motor organs. — The motor organ in leaves is usually 
the leaf base (^[ 151) or a modified portion of the petiole, 
sometimes greater but generally less in diameter than the 
rest. Its cortex consists of large, rather thick-walled, pa- 
renchyma cells, and the stele occupies a relatively small part 
of the transverse section. In other parts of the petiole the 
stele is much larger, or there may be several steles distributed 



THE MOVEMENTS OE PLANTS. 



205 



about the center. (See ^[ 164. ) 
show the contrast. If the leaf 
be a compound one, there are 
usually secondary motor or- 
gans at the base of the leaf- 
lets, as in the leaf of the bean 
(fig. 202). Variation in the 
turgor of the cells of the cor- 
tex upon one side or the other 
produces a sharp curvature of 



In figure 



I and B 





Fig. 201. Fig. 202. 

Fig. 201. — Transverse sections through petiole of scarlet runner, ./.through the rigid 
portion; B, through the motor organ. G, g, vascular bundles; .. cortex; w, pith; 
r, deep channel along ventral siiU- oi petiole. Magnified about 10 diam.— After Sat hs. 

Fig. 202. — Portion ol .1 scarlet runner, which, originally growing erect, has been inverted 
for several hours, resulting in geotropic curvatures ol the primary motoi organs /', /"', 
l n . The lowest pair oi leaves show secondary motor organs at the juncture of petiole 
and blade. Similar ones are present in the upper compound leaves, but are not . lcarly 
shown in the figure. The arrows show the position oi the petioles when the plant was 
first inverted. About two thirds natural size —After Sachs. 

the motor organ, which alters the position of the leaf or leaflet 
(fig. 202). The concave surface of the motor organ is always 
deeply wrinkled transversely, while the convex surface is 
smooth. 




206 PLANT LIFE. 

296. Spontaneous movements. — Only a few plants exhibit 
spontaneous movements through the motor organs. The lat- 
eral leaflets of the telegraph plant (s, fig. 203), under normal 

conditions of rather high temperature (at 
least 22 C), show jerky movements of 
such direction that their tips describe an 
irregular ellipse, which is completed in 
1 to 3 minutes. The leaflets of the 
clovers and oxalis show much slower 
movements (of a few hours period), 
which are usually obscured by the light 
movements described in the next para- 

Fig. 203. — Leaf of Hesmo- ____t, 
diu.l gyrans. Two graph. 

Sa , c r hs natural slze ~ After More commonly the turgor movements 
are induced. The most common stimuli are light and con- 
tact, although many others suffice to induce them. 

297. Photeolic movements. — Movements produced by the 
withdrawal of light have long been known as "sleep move- 
ments ;" more properly, photeolic movements — that is, move- 
ments induced by variation of light. They are best observed 
upon the leaves of the bean family, though many other plants 
exhibit them. Figure 204 shows the positions assumed by 
various leaves toward nightfall. It will be seen that in 
compound leaves the leaflets sometimes rise, so as to apply 
their outer faces to each other ; others sink, so that the un- 
der surfaces are in contact ; others become folded in various 
ways. This position is maintained throughout the night. 
Upon the increase of light in the morning, the day position 
is assumed. The cutting off of light artificially from any of 
these plants causes them within a short time to assume the 
nocturnal position. Darwin suggested that the nocturnal 
position prevents the loss of heat by radiation and consequent 
injury from light frosts. But it is not by any means certain 
that this is its real purpose. 



THE MOVEMENTS OF PLANTS. 



207 



298. Contact movements. — Some organs arc sensitive to 
contact, as the leaves of Venus' fly-trap and other related 
plants. The motor organ in the Venus' fly-trap (figs. 386, 
205) is the cushion of tissue running along the dorsal side of 
the leaf between the two lobes. By the sudden variation in 




Fig. 204. — Photeolic movements, a, leaf of a mimosa in day position ; a', the same in 
night position. />, leaf of Coronilla varia in day position ; />', the same in nighl po- 
sition, r, leaf of A mor&ka fruticosa in day position ; <■'. the same in night position. 
</, leaf of Tetragonolobus in day position ; </', same in night position, — Alter Kemer. 



turgor of some of these cells the two halves of the leaf are 
thrown quickly together when one of the six bristles upon its 
upper surface is touched. The sensitise plant drops one of 
its leaflets or the whole leaf quickly when stimulated by con- 
tact, heat, or electricity. The position of the leaves when 



208 



PLANT LIFE. 



normally expanded is shown in figure 206, and their position 
after stimulation by figure 207. The stamens (^[ 344) of 
some flowers and the stigmas (^j 336) of others are sensitive 




Fig. 206. Fir,. 207. 

Fig. 205. — Part of a transverse section of a leaf of Venus' fly-trap, in, the cushion of 
tissm- constituting the motor organ ; />, one of the sensitive bristles which, upon being 
touched, cause the leaf to close ; /, one of the interlocking teeth. The minute pro- 
jections over inner (ventral) surface are glands which secrete the digestive fluid and 
later absorb the food. Magnified about 5 diam. — After Kurz. 

Fig. 206. — A leaf of the sensitive plant fully expanded. Natural size. — After Duchartre. 

In.. 207. — A leaf of the sensitive plant after stimulation. The motor organ at the base 
of each leaflet has thrown it forward and upward ; the motor organs at the base of the 
four divisions have moved them together. The motor organ at the base of the main 
petiole has moved the whole leaf sharply downward. Natural size. — After Duchartre. 

to a touch, shortening, elongating, or bending in such a way 
as to promote pollination (*| 358). 

The motor organs of the leaves of a number of the bean 
and oxalis families also react to more violent mechanical 
stimuli. Their movements are similar to those described in 
U 2 97- 



PART III: REPRODUCTION. 



CHAPTER XVI. 

INTRODUCTION. 

Having considered in Parts I and II the structures and 
functions by which the nutrition of the individual is secured, 
Part III is devoted to the consideration of the structure and 
functions of the reproductive organs and the functions by 
which a succession of similar individuals is insured. 

One of the fundamental powers of protoplasm is its ability 
to produce new organisms as offspring from the older ones. 
In the simpler plants the two great functions, nutrition and 
reproduction, are often carried on by the same cell. This 
must always be so in the unicellular plants. In the higher 
plants, however, these two functions become completely sep- 
arated, organs being specialized for each, so that the func- 
tions may be more certainly and efficiently performed. 

299. Reproductive structures. — Any part capable of grow- 
ing into a new individual may be called a reproductive body, and 
the part on which or in which it is produ* ed is a reproductive 
organ. If the reproductive bodies consist of one or two cells 
only, they are usually called spores, [f they are cell-aggre- 
gates, they are generally called brood buds or gemmce i to dis- 
tinguish them from ordinary buds. In both cases it is neces- 
sary that the cells to be separated from the parent should be 
capable of growth — that is, in the condition known as the 
embryonic phase (•[ 256). The reproductive organs pro- 

209 



2IO PLANT LIFE. 

duced by some plants are exceedingly complex and varied, 
while others form reproductive 1 todies in very direct ways. 
The reproductive bodies themselves are generally very simple. 
In addition to complex reproductive organs, there are some- 
times accessory parts by which the plant adapts its reproduc- 
tive functions to the conditions under which it lives. Among 
these accessory structures are many, as among the flowers of 
seed plants, by which the aid of other plants or animals is 
secured. 

300. Vegetative and sexual reproduction. — In all the 
diversity of organs and processes two chief methods may be 
distinguished, called vegetative reproduction and sexual repro- 
duction . 

Vegetative reproduction consists in the formation of repro- 
ductive bodies by processes of growth only. The modes in 
which they arise are varied in detail, but consist essentially 
in the production by the parent of a body, unicellular or 
multicellular, which at maturity develops, under suitable 
conditions, into a new plant. 

Sexual reproduction consists in the formation of reproduc- 
tive bodies by the union of two specialized cells, neither of 
which alone is capable of developing into a new plant. 



CHAPTER XVII. 
VEGETATIVE REPRODUCTION. 

I. Fission and budding. 

301. Fission. — In single-celled plants cell division and 
reproduction are practically identical, since shortly after divi- 
sion occurs the two cells so produced separate and lead an 
independent existence (C, fig. 18). Such a method of repro- 
duction evidently interferes little with the processes of nutri- 
tion, which probably are scarcely even suspended during the 
process of reproduction. 

302. Budding. — A slight variation of the method of fission 
just described is to be found in those single-celled plants, 
such as the yeasts, whose growth is so localized as to form 
upon one side a small enlargement which ultimately attains 
the size of the parent, with which it is connected by a very 
narrow neck (fig. 48). Across this neck the partition wall is 
formed in the usual way. This becomes mucilaginous, ren- 
dering the adhesion of the daughter cell at this point so weak 
that it is easily separated from the parent. This method of 
reproduction is known as budding. 

303. Fragmentation. — In those plants which consist of 
a row of cells more or less closely united, the breaking up of 
the filaments into separate pieces, either through externa] 
force or the death of one of the cells, may produce a number 
of smaller colonies or of new individuals, each of which may 
grow to full size. In some of the more looselv organized 
filament-colonies, such as Nostoc (see • 13, and figs. 1 }, 
14), there are specialized cells whose function seems to be 

21 1 



212 PLANT LIFE. 

to loosen pieces of definite length, which creep out of the 
jelly, grow, and thus produce new colonies. 

The greater size reached by most multicellular plants soon 
renders impossible the continuance of this method of repro- 
duction, except among those whose cells arc all alike. Should 
such separation into nearly equal parts occur among more 
highly specialized plants, it is evident that one portion might 
easily be left without nutritive organs adapted to its needs. 
The higher plants, therefore, specialize certain regions or 
members, where, by division or budding or similar processes, 
reproductive bodies may be formed. 



II. Spores. 

304. Sexual and non-sexual spores. — A spore is a single- 
celled body capable of producing a new plant. Spores may 
be formed either by a process of growth or by a sexual act — 
i.e., the union of two cells. The former are called non- 
sexual spores ; the latter, sexual spores. Only non-sexual 
spores are discussed in this chapter. 

305. Structure. — While a spore is generally composed of 
one cell, the term is extended to include two- to many-celled 
bodies which are formed in the same way as the simpler 
ones. In fact, no clear distinction in form or structure can 
be drawn between spores and brood-buds. (See 1" 361.) 

306. Motile spores. — Spores may be either naked and 
motile or furnished with a cell-membrane and non-motile. 
The former are commonly produced by plants which pass all 
or part of their lives in water, such as the algre and aquatic 
fungi. They are usually pear-shaped and furnished with one 
or more cilia, by means of which they swim about (fig. 168). 
When locomotion was supposed to be a distinctive power of 
animal bodies they were called zoospores, a name still re- 
tained. They are also called swarm-spores. 



VEGE TA Tl I E REPROD UCTION. 



213 



When zoospores possess chlorop 
quently do, they are aggregated at 
the larger end, leaving the pointed 
end to which the cilia are attached 
colorless. Zoospores are formed 
either in a general body-cell, not 
visibly different from the other 
body-cells, or in a cell specialized 
in form and structure. In either 
case the cell in which they are pro- 
duced is called a zoosporangium. 
The entire contents of the zoospo- 
rangium may form a single zoospore, 
or it may divide into several or 
many. In the latter case the nu- 
cleus divides into two or more, each 
of which gathers about itself a por- 
tion of the protoplasm. The zoo- 
spores are set free by the rupture of 
the wall of the sporangium or by 
the solution of a portion of the wall 
(fig. 208). They may begin to 
move before the rupture of the wall, 
in accomplishing which their activ- 
ity may materially assist. They 
then work their way out and swim 
freely in the water. After a time 
of movement they usually lose their 
cilia, either withdrawing them into 
the protoplasm or dropping them 
off, come to rest, and begin to grow 
into a new plant. 

307. Non -motile spores are 
formed by all classes of Land plants 




l'n. 208 -Development and escape 

of zoospores of an aquatic fungus 
{Saprolegnia lactea). The ends 

ot two hvph.e are shown, the ter 

minal cells being goosporangia 

In ,;. the protoplasm 1 

ing about the numerous nui lei (no 

shown). From 6 many ol tin- ZO 
ospores have escaped through the 
perforation in the wall near the 

upper end of tin- .ell. From ."11 

have est aped hut one. whk h is just 

slipping through the opening ( here 

in profile). Magnified 300 diam. — 

Aftei kerner. 

without exception. They 



^■4 PLANT LIFE. 

are often produced in great profusion, especially by the fungi, 
the mosses, the ferns, and the seed plants. 

308. Form and structure. — Their form is exceedingly 
various. Many are spherical or ovoid, while some are cylin- 
drical or even needle-shaped (figs. 213, 228, 271). Irregular 
forms, also, are not uncommon. 

In structure spores are usually only single cells, specialized. 
Each is a nucleated mass of protoplasm surrounded by 
a cell-wall which may be either thin or thick, according 
as the spore is destined to immediate growth, or, as a 
resting spore, to endure for a time unfavorable conditions. 
In some cases the wall of even the 
' ') JL[\ A -'Jf/fr thin-walled spores has two layers, a 
condition which is almost universal 
among resting spores. When the 
wall is so differentiated the inner 
layer is delicate, rarely thickened, 
extensible, and composed of more or 
less unaltered cellulose. The outer 
layer is often irregularly thickened, 
so that its surface is covered with 

Fig. 2 oo.-Section of a mature ria ^es, WartS, Spines, Or boSSCS of 

rt"el^of^fdf(co& various sorts (figs. 210, 248, 271, 
u;r!-rVu; e t tcZ,.^'u 1 e'399)- " is brittle, as compared 
S^pma^tT^ndiwith the inner coat, and is usually 
^ V ed a To«t ati so St diaS re -fe-more or less altered in composition 
from its original cellulose nature. 
A third layer (the epispore) is sometimes present, but this 
is not produced by the cell which it surrounds. It is added 
from the outside, being derived from the protoplasm sur- 
rounding the spores after they are formed* (fig. 209). This 
form of spore is common among the fern allies. 

* This protoplasm often comes from the disorganization of some of the 
tells around the chamber in which the spores lie. 




VEGETATIVE REPRODUCTION. 



215 



309. Food. — In almost all cases there is a supply of reserve 
food within the spore. This reserve food varies in amount 
with the conditions under which the spores are formed. It 
is ordinarily greater in resting spores than in those intended 
for immediate growth. Spores may contain chlorophyll, but 
generally do not ; even the spores of green plants are mostly 
without it. Its presence seems to indicate an active condition 
of the protoplasm, and the vitality of such spores is usually 
of short duration. It is of course absent from the spores of 
colorless plants, such as the fungi. 




Fig. 210. — Part of a vertical section of a leaf of a willow, attacked by a fungus (.!/<•/<!»//- 
sora salicimi). eo, epidermis of upper side lifted by the young teleuto spores; /, de- 
veloping from the spore-bed above the ends of the palisade parenchyma, />nr ; en, 
epidermis of the under side, broken through spore-bed from which spring uredo- 
spores, st. and paraphyses, /•. eo will also finally be ruptured to set free /. Magni- 
fied 260 diam. — After Prantl. 

310. Growth. — Spores germinate by absorbing water, thus' 
bursting the more rigid layer or layers of the cell-wall. The 
inner layer then grows in area to accommodate the increas- 
ing protoplasm, which so controls the regions of growth and 
the mode of cell division as to produce a plant of definite 



216 



PLANT LIFE. 



form. In many cases the plant produced is essentially like 
that which gave rise to the spore. In others it is different, 
but sooner or later in the life cycle the same form recurs. 
Variety of bodily form is common among the fungi, in which 
it is called pleomorphism. Among plants showing well-de- 
fined alternation of generations ( r€ ; 55, 320), the non- 
sexual spores are produced by one form only, and always 
give rise to the other. 

311. Origin. — Non-motile spores are either free, being 
produced at the ends of branches specialized for that purpose, 
or enclosed in a case called a sporangium. Often the same 
plant forms spores by both methods at different stages in its 
development. 




Fig. 211. — Diagrams showing the formation of an acropetal sin.iicli.iiii by budding. 
a, the spore-producing hypha : b, its terminal c < • 1 1 showing a bud which in c has ma- 

tured into .1 spore ; (t, the spore < has budded, anil so on, until in h five spores have 
been formed, numbered in order of their development.- Alter Zopf. 

312. Free spores. — The formation of free spores is con 
fined to the lower plants, and is especially characteristic of 
the non-aquatic fungi. The branches producing spores may 
occur singly, or, more commonly, they are aggregated at 
certain points, forming a spore-bed (fig. 210). If the fungus 
develops its mycelium in the interior of a host, the formation 
of a spore-bed is often necessary to rupture the host, so that 



V EG ETA TIVE REP ROD UCTION. 



217 



the spores may be brought to the surface and set free. Thus 
the spore-beds of parasitic fungi commonly blister the surface 
of the host by lifting up its outer tissues (eo, fig. 210). 

313. Spore-chains. — Spores maybe produced either singly 
at the ends of the branches or in chains. When produced in 
chains, the youngest spore may be at the base or at the apex 
of the chain. The first method is much more common than 
the second. In the second case each spore must arise as a 
bud upon an older spore, budding itself to form a younger one 
(fig. 211). The spores in such a chain are limited in number. 
They develop rapidly, and all are loosened at about the same 
time. Those chains which have the oldest spore at the apex 





Fig. 212.— An outline showing the formation oi a basipetal spore-chain of the blue-green 
mold i Penicillium glaucum), 6, branch oi spou- hearing hvpha. budding beneath 
two older spores. Across the narrow net k a partition wall is formed, the spores round 
off, and from this wall a device, .. for loosening the spores is developed. The 
terminal spore is oldest. Highly magnified.- Alter Frank. 

Fig. 213.— Longitudinal section through the edge oi a gill of a mushroom (Cofrinus) 
after spore-formation is completed. /, interwoven hyphae ol the gill, branching to 
form the hymenium, composed ol the paraphyses, /, the cystidia. < . anil the ba- 
sidia, /'. The latter give rise to tour slender I nam lies, ulmsc tips enl.uge 1" lorm each 

a single spore, /and. do not produce spores. Magnified 300 diam.- Alter Brefeld. 

arc produced by the continued division of the branch by 

transverse partitions, usually preceded by budding of the 
apex, often described as constriction (/>, fig. 212). Beneath 



2l8 



PLANT LIFE. 



the first spore so formed another spore is produced as the first 
grows older ; and this process continues as long as the 
plant is able to furnish material for the making of spores. 
In such cases, often the oldest spores are liberated while 
new ones are being produced at the base of the chain. 

A modification of the production of spores singly occurs 
when the branch destined to produce them gives rise to 
two to eight very slender branches, each of which enlarges 
at the tip into a single spore, so that the main branch appears 
to carry two to eight spores upon slender stalks. Such a 
spore-producing branch is called a basidium (fig. 213). It is 
the characteristic form in the higher fungi, which produce 
conspicuous fructifications. 




Fig, 214. — A, a puffball (Octaviana) halved, showing the internal chambers (shaded 

dark) lined by hymenium (the narrow white border). The intervening spaces, g, 
and the unshaded outer part are formed of interwoven hvph.i . Magnified 5 diuin. 
/>', a bird's-nest fungus (Crucibulum) halved. The similar internal chambers have- 
been loosened by the disappearance of the intervening hyph.e immediately about the 
hymenium (represented by radiating lines) and a wavy Stalk by which each remains 
loosely attached. Magnified 4 diam. — After Luerssen. 



314. Fructifications. — In the higher fungi whose myce- 
lium is developed within a dead substratum many brant lies 
are aggregated to constitute a reproductive structure or fructi- 
fication, which is the only conspicuous part of the fungus. 
(For an account of the vegetative parts, see ^]^[ 50, 54.) 



VEGE TA TI J 'E RETROD UCT10N. 



219 



The body of the fructification is made up of hyphae, more 
or less interlaced and adherent, and is of a form adapted, not 
only to break through the substratum, but also to furnish an 
extensive surface for the spore-beds, called in these plants the 
hymenium (fig. 213). The hymenium consists of the enlarged 




Fig. 215. 
Fig. 215. — A fructification of Clavaria 
a i< > t\i. The hymenium covers the 
upper part of the branches. Natural 
size.— After Kerner. FlG. 216. 

Fig. 216. — A fructification of a mushroom, Amanita phalloides. /. the cap or pileus ; 
?■, the veil, originally connected with edge of cap, covering the gills which radiate tnun 
the stipe, st, to the edge of cap; vo, the volva. The surface ot the gills is covered 
with the hymenium. Most mushrooms showing a distinct volva are poisonous. 
Natural size. — After Kerner. 

free ends of the hyphae, which are set at right angles to the 
surface. Some, the basidia, develop 2-S slender branches 
each of which produces at the tip a single spore. The hyme- 
nium may be formed upon the outer surface of the fructifica- 
tion or in internal chambers (fig. 214). In the latter case 



220 



PLANT LIFE. 



these chambers rupture at the maturity of the spores, or even 
earlier. 

The fructification may be irregularly lobed, sessile and 
gelatinous, or much branched and cylindrical or flattened, 




Fig. 217. — Fructification of Hydnum imbricatum. 
The surface of the projecting spines on the under 
side of the cap are covered with the hymenium. 
Natural size. — After Kemer. 



with the hymenium covering the 
whole or the upper part of the body, 
as in Clavaria (fig. 215)5 or it may 
form an umbrella-like, stalked cap, 
as In toadstools, with the hymenium 
extending over radiating plates on 
the under side of the cap, as in - \gari- 
cus (fig. 216), or over spine-like pro- 
jections in the same region, as in 
Hydnum (fig. 217); or it maybe 
a semicircular, sessile body projecting 
from the substratum like a shelf or 
bracket, with the hymenium lining 




w &i 



Fig. 218.— Trunk of an ash tree, 
showing fructifications of Poly- 
porus ig na rius. Alter a pho- 
tograph by Von Tubeuf. 

innumerable minute 



VEGETATIVE REPRODUCTION. 221 

tubes on the under face, as in Polyporus (fig. 218) ; or it may 
take the form of a ball, the hymenium arising as a lining 
upon the walls of regular or irregular internal chambers, 
which may occupy most of the interior, as in puffballs and 
their kin (figs. 214, 219). 

315. Sporangia. — Spores are also formed in the interior 
of cells which are either free or covered by a jacket of other 



Ik Hs 



KW 




1^ 



Fig. 2ig. — Fructification of a puffball (Geaster hygrometricus) \ A , young ; />', mature, 
the outer layer split open and recurved, the inner also broken to allow escape of 
spores. Natural size. — After Corda. 



cells. The entire structure is called a sporangium. In the 
first case the sporangium is said to be simple. Its wall is the 
wall of the mother cell in which the spores are produced, 
and they are set free by its rupture (fig. 220). In the second 
case the sporangium is said to be compound. The mother 
cells of the spores (rarely only one mother cell) are sur- 
rounded by others forming a jacket of greater or le>s thick- 
ness. In the mother cells, which are differentiated from the 
investing cells, the spores are formed as in simple sporangia. 
As the spores mature the walls of the mother cells burst or 
are disorganized, leaving the spores still surrounded by the 
layer or lasers of investing cells (fig. 221). This jacket is 
ruptured sooner or later and the spores, thus set free, are 
distributed in various ways. (See % 475.) 



222 PLANT LIFE. 

316. Simple sporangia. — The simple sporangium may 
be like the general body-cells, or it may be specialized in 





Fig. 220. — Longitudinal section of the simple sporangium of a mold (Mttcor). The 
aerial hypha, //, has partitioned off a cell, .r, within which spores are produced. The 
walls of this sporangium are studded with needle crystals of calcium oxalate. The par- 
tition protrudes far into the end cell. Magnified 260 diam. — After Kerner. 

Fig. 221. — Longitudinal section of the stem, s, of a moss gametophyte, bearing leaves, 
b. Embedded in the stem is the sporophyte, consisting of a stalk, st , and a compound 
sporangium, of which w is the wall, formed of a sheet of cells, enclosing the spores, 
sp (contents not shown). Magnified 100 diam. — After Hofmeister. 



form as well as in function. It may be spherical, sac-like, 
or linear. The elongated sporangium produced by the en- 
largement of the end of a hypha in certain fungi has received 
a special name, ascus. The number of spores formed within 
a simple sporangium may be two or more, up to several 
hundred. The spores are formed like the zoospores de- 
scribed in ^[ 306, with the difference that a wall is secreted 
by each spore be/ore it escapes. 

The rupture of the tell wall, which sets the spores free, 
is brought about by the increase of the spores in size, or by 
the swelling of the surplus protoplasm left after their forma- 
tion. Preparatory to bursting, the wall is frequently altered 
so as to be mucilaginous, or it becomes brittle. In some 
cases a certain area is thin, which furnishes a starting-point 
for the rupture. 



V EG ETA TIVE REPRODUCTION. 



223 



317. Arrangement. — Simple sporangia may occur singly 
or they maybe aggregated. When 
aggregated, they usually stand side 
by side, and constitute a layer, 
called the hymenium (figs. 222, 
226). (Compare If 314.) When 
thus aggregated (and even when 
single) they may be enclosed by 
a jacket formed by the coalescence 
of sterile filaments, as in the mil- 
dews, in which the whole structure 
constitutes a fructification (figs. 
223, 224, 337). In the lichens the 
hymenium, during its earlier stages, 
is partially enveloped by sterile 
filaments forming a cup-like apo- 
thecium (figs. 225, 226). In the 
cup fungi (fig. 222) the fructifica- 
tion, which is the only part of the 
fungus above the substratum, is a 
single apothecium, whose whole 
inner face is the hymenium. In 
an allied form, the morels (fig. 
227), the fructification is differ- 
entiated into a stalk carrying an 
enlarged head marked by narrow 
ridges separating broad shallow pits 
over the surface of these depressed areas. In other fungi, 
the sporangia are sunk in deep, narrow-mouthed pits with 
which the outer part of the fructification is filled ( fig. 22S). 

The simple sporangia of some of the red seaweeds show a 
transition to the compound type in being formed by an in- 
ternal cell of the thallus (fig. 229). The adjacent cells, how- 
ever, do not constitute a special wall, nor are they neces- 




[G. 222. — A cup fungus {Peziza 
aurantid). A, three fructifica- 
tions, about natural size. The 
inner surface of the cup is covered 
with a hymenium, a bit ol which 
is shown' at />' in section at right 
angles to surface. /•, paraphyses ; 
,;. an asms bursting to allow 
escape of spores. Highly magni- 
fied—After Keriler. 

The hymenium extends 



224 



PLANT LIFE. 



sarily ruptured to permit the escape of the spores, being 
often displaced in the development of the sporangium, so 
that at maturity it is partially free. 




Fig. 223. — A mildew (Erysipke communis), showing the mycelium ramifying over a 
bit of leaf, with erect spore-bearing branches and globular fructifications, containing 
asci. Magnified about 175 diam.— After Tulasne. 



318. Compound sporangia. — Simple sporangia occur only 
among the lower plants. In the higher plants, including 
the mossworts, fernworts, and seed 
plants, the sporangium is always 
compound. 

319. Development. — ( Compound 

sporangia may be developed either 

from superficial or from internal 

.. fr ! ,m cells. As a consequence, the mature 

the interior of the fructification ■ 

rxa\&vn<ErysipkeHeraciei\ sporangia will be either free or more 

similar to those shown in fig. 223. ' n 

Each as, us contains four spores. or l ess enclosed within the tissues of 

Magnified 200 diam. — After De- 

Bar y. the organ by which they are borne. 

A superficial cell may enlarge so as to protrude from the 

surface, and divide into two parts, of which the upper cell 

develops into the sporangium proper, and the lower cell into 

its stalk. According to this method of development the 

sporangium is a surface appendage, and may be looked upon 




VEGE TA 77 1 E RETROD UCTION. 



225 



as homologous with a hair. Sometimes the sporangia, 
although really free, are overgrown by adjacent parts, so that 




Kig. 225.— A lichen {Parmelia conspersa) growing on a stone, showing the leaf-like 
thallus (.mycelium 1 , with many fructifications lapothecia 1 . The older ones are more 
or less irregular and large with a narrow rim ; the younger are nearer the margin, cir- 
cular, and nearly closed over at top. Natural size. — After Frank. 




Fig. 226.— A vertical section of an apothet ium ol a li( hen 1 , \ naptychia ciliaris). h, 
the hymenium; y, the subhymeruum, a layer. .1 densely interwoven hyphae; .-. r, the 
sterile' hyphae which partially enclose the hymenium ; rn, the loosely woven hyphae <>t 
the thallus; a, the algae enslaved by the fungus, Magnified about 50 diam.— After 

Sachs. 

they are enclosed in a chamber, whence the spores est apt- 
after they are set free by the bursting of the sporangium. 



226 



PLANT LIFE. 



The other mode of development produces enclosed spo- 
rangia. One or more internal cells differentiate and become 
the mother cells of the spores. The spores, when mature, 




Fig. 228. 



Fir.. 227. — A fructification of the morel (Morchella esculentd). The hymenium occu- 
pies the surface of the depressed areas. Natural size. — After Kerner. 

FlG. 228.— A small bit of a section through the fructification of the ergot (Claviceps 
purpurea), showingone ol the deep, narrow-mouthed pits, P (and part of another), 
enclosing the asci. From the broken ascus at the right thread-like spores are escap- 
ing. Highly magnified. 



-Alter Tulasne. 



will therefore be enclosed by the adjacent cells of the plant, 
which may became altered so as to form a sort of special wall 
more or less different from the tissue which lies farther off. 



VEGE TA TIVE REPROD UCTION. 



227 



320. The sporophyte. — Among the mossworts, fernworts, 
and seed plants reproduction by non-sexual spores has be- 
come so fixed and important that 
one stage in the plant is devoted 
especially to producing them. 
This phase is different from that 
producing sexual cells, the differ- 
ence becoming greater the more 
complex the plant. The stage set 
apart for spore production is called 
the sporophyte. In the moss- 
worts the sporophyte has very 
little green tissue, and therefore 
carries on little nutritive work, 
but depends for its supply of food 
chiefly upon the sexual stage, with 
which it is connected throughout 
its entire existence (^| 68). In 
the fernworts and seed plants, 
however, the sporophyte possesses 
extensive nutritive tissues, the 
leaves, stems, and roots belonging 
entirely to this stage. Sporangia 
in these plants may be formed 
either upon the stem or the leaves 
— never upon the roots. 

321. Liverworts. — In the 
liverworts the sporangium is gen- 
erally produced at the upper end 
of a short or long stalk. It is 
either spherical, ovoid, or short- 
cylindrical (figs. 64, 65). The 
spore-producing tissue occupies the greater part of the 
interior, the wall being formed usually by a single layer of 




. 229. — A branch <>i .1 rul mm- 

ing tetn isp. .us. .', formed bj an 
interna] cell of the thallus Mag 
nifiedabout loodiam. -AfterKUtz 

ing. 



228 



PLANT LIFE. 



cells. Mixed with the spore-producing cells, however, arc 
many sterile cells, which become gradually elongated, and 



spm 




Fig 



-The i 



phyte of a peat moss {Sphagnum acuti/blium)vntb adjacent parts 
of thegametophyte. The spun .phyte consists of a capsule, -u'. and a broad foot, sg", At 
the stage shown in />' it is still completely enclosed in the tissues of the gametophyte, 
viz., c, the enlarged ovary which forms the calyptra or hood, and v, the vaginule or 
sheath surrounding the foot, ar is the neck oi the ovary. (Compare fig. 331 I The 
ajc over the large-celled central tissue (columella) is the sporangium, fit, the false 
stalk, produced by the gametophyte, which raises the sporopnyte. [n A, the calyptra 
has broken, only a fragment remaining, exposing the capsule. ' d, the lid. by whose fall 
the sporangium is exposed and the spores escape. , h, leaves oi the gametophyte : qt, 
the false stalk. Compare figs. 67, 72. 73, in which the stalk is part oi the sporophyte. 
. I magnified 13 diam.; /■'. 32 diam — After Schimper. 
FlG. 231. — Longitudinal section of the young capsule of a true moss (Bryum), s, spo- 
rangium. At this stage the mother cells 01 the spores, spin, have become free (only a 
few are shown still enclosing the spores): tw, the wall of the sporangium, lined by 
the remains of another layer of cells now disorganized ; < , the columella, of partly col- 
lapsed cells ; it, intercellular space : cm, wall of the capsule : .1 n, the annuius, a ring 
of cells which pries off the lid, at whose edge they develop : ot, the outer, in, the inner, 
peristome, formed by the thickening of parts of the walls of certain rows of cells; >/.', 
nutritive tissue, with chloroplasts and intercellular spaces. Magnified 25 diam. — Orig- 
inal. 



VEGETATIVE REPRODUCTION. 229 

in many species thicken their walls along one or more spiral 
lines. These sterile cells are called elaters (fig. 11, A, A'). 
They serve to entangle the spores in dusters when they are 
set free. The sporangium opens at maturity by splitting at 
the apex, sometimes into two, commonly into four or more, 
parts (fig. 64). 

322. Mosses. — In most mosses the sporangium is developed 
within the enlarged upper part of the sporophyte, to which 
the name capsule is given. In the peat mosses it is cap- or 
thimble-shaped (fig. 230), while in most of the true mosses 
it is a hollow cylinder (fig. 231). It opens by the falling off 
of the sterile upper end of the capsule, which separates as a 
lid and thus allows the spores to escape from the upper 
end of the cylindrical sporangium. By the time the spores 
are mature, the sterile central tissue of the capsule, which 
forms the columella (c, fig. 231), shrivels and often almost 
disappears, so that the capsule seems to be a cup or urn, filled 
with loose spores. In the younger stage (fig. 232) the orig- 
inal form is shown. 

323. Ferns. — In the ferns the sporangia are usually nu- 
merous, stalked, free, and often associated in clusters 
called sori. They are either produced upon the under sur- 
face of the foliage leaves or upon specialized leaves.* The 
sori are often arranged in elongated clusters or lines 
(fig. 2$$). Each sorus, or a (luster of them, may be pro- 
tected by a special outgrowth from the cells in its neighbor- 
hood, called an indusium (tigs. 233, 234). Each sporangium 
consists of a stalk composed of two or four rows of cells ex- 
panding above into a body composed of a single outer layer 
enclosing the spore producing cells, and at maturity the 
spores themselves. The walls of a row of cells more or less 
completely encircling the body of the sporangium become 

* It must l>o remembered that the entire plant, consisting of root, stem, 
and leaves, is the homologue <>f the capsule and sialk <>!' the mossworts. 



230 



PLANT LIFE. 



irregularly thickened (sec fig. 401). The strains caused by 
the unequal absorption and loss of water burst the sporangium 
at some definite point. This 
Line of dehiscence is often 
between a pair of large sad- 
dle-shaped cells (fig. 401). 

324. Sporophylls. — In 
many of the ferns the leaves 
which produce sporangia are 
not different from the foliage 





Fig. 233. 

Fig. 232. — Diagram of a longitudinal and transverse section of the very young capsule 
of a true moss (Bryum). The transverse section is taken along the line A B. a, the 
mother cells of the spores ; < . the columella ; is, intercellular space. The constriction 
at the top marks the limit of the lid. The part below the sporangium is the neck, with 
nutritive tissues. — Original. 

Fig. 233. — A leaflet of a fern (As/- id in in) seen from the back. Eight sori are shown, 
each covered by its own indusium, /. Magnified 2 diam. — After Sachs. 



leaves. . In others, certain leaves are so specialized for 
bearing the sporangia that they lose their nutritive function 
in part or entirely. To such spe< ialized leaves the name 
sporophyll is applied. 

325. Horsetails. — In the horsetails the sporangia have the 
form of sacs, varying in number from six to twelve. They 
arise upon the lower face of a shield-shaped sporophyll (figs. 
2 35» 2 3 () )- These sporophylls are aggregated in a close 
cluster at the upper end of the axis, constituting what 



VEGETATIVE REPRODUCTION. 2$\ 

may be called, properly enough, a flower.* The wall of the 
sporangium when young is formed by three layers of cells, 
but consists at maturity of one layer only, which, having its 
cell-walls thickened in an irregular manner (fig. 238), tears 
open the sporangium, usually along a vertical line. The wall 
of the spore consists of three layers, the outer one splitting 
into narrow strips and remaining lightly attached to the spore 
at one point (fig. 239). To these parts of the cell-wall the 
name elaters has also been given. (Compare 1" 321.) Their 




Fig. 234. — Vertical section through the leaflet shown in fig. 233, passing through the cen- 
ter of a sorus. e, ventral epidermis; <■', dorsal epidermis; between them the meso- 
phyll, showing 3 veins cut across; over the central one is a cushion of tissue from 
whose surface arise the stalked sporangia s, s. i, i, the indusium. Magnified about 30 
diam. — After Sachs. 

purpose seems to be to entangle the spores so that they may 
not be too sparingly distributed. 

326. Club-mosses. — In club-mosses the sporangia are sac - 
like outgrowths upon the upper surface of the leaf near its 
base, or occasionally of the axis itself jusl above the leaf. 
Sometimes the leaves bearing them are the ordinary foliage 
leaves ; in other species they are specialized and crowded 
into a terminal (luster or spike (fig. 240). 

327. Differentiation of spores. — Among the higher fern- 
worts tlie spores are of two sizes : large ones, known as mega- 

* This term is not generally applied to those sporophylls. Rut see defi- 
nition of a flower, % 320, and compare tig. 237 of a " flower" of Zamia. 



23: 



PLANT LIFE. 



spore's, and much smaller ones, known rs microspores (fig. 
241). Each kind, when it germinates, produces a sexual 
plant, or gametophyte (■ 377), upon which, however, only 




Fio. 235. 



Ki<;. 



Fir,. 235 Pari ol two sporophytes ol .1 horsetail {Equisetum arvense). A, the 
spring shoots, with sheath like whorls ol leaves below and crowded sporophylls above 
«, summer shoots, much branched, with inconspicuous leaves; nutritive work all 
done by stems ..i these shoots. Two thirds natural size After Kerner. 

Fig. 236. — Three sporophylls from the flower of a horsetail {Equisetum telmntein), 
seen in different positions, s, the shield-shaped sporophyll ; st, its stalk attached to 
the center of dorsal face ; sg; sporangia. Magnified about 10 diam.— After Sachs. 



one sort of sexual organs is borne. The megaspores give rise 
to plants bearing female organs only, the microspores to 



VEGE TA TI I 'E RETROD UC TION. 



233 



those bearing male organs only. A similar separation of 
sexes in the gametophytes frequently occurs when the spores 
are equal in size, as in Marchantia and horsetails, but it 





ri<;. 237. 

Fig. 237- -A, the " flower " of a seed plant (Zamia muricata). It is 1 omposed of 
crowded sporophylls, of which one is represented in A' as seen from the side. It has 

a stalk capped by a hexagonal tup, .>. with numerous sporangia, 1 . on the under side. 
. I , natural size. ' ti, magnified about 6 diam Aftei Karsten, 
Fio. 23S. — A bit of a section of the wall of a sporangium of a horsetail The cells of 
the outer layer thi< ken their walls along spiral lines. The two inner layers of CI 

become disorganized at maturity ol the sporangium. Magnified 250 diam \tt.r 

( 'ainpbell. 

I'll.. 239.— Two spores of a horsetail [Eguisetum arvense); one showing thi elaters 
open, as when dry, the other with them coiled, as when moist. Magnified 25 diam. — 
After Kerner. 



234 



PLANT LIFE. 



always occurs when they are unequal. A corresponding dif- 
ference in size is often found between the sporangia con- 
taining small spores (microsporatigia) and those containing 
large spores (megasporangia) (figs. 241, 242 1. 

The sex terms, male and female, applicable primarily to 
the sex cells, arc applied also to the organs and to the plants 




240. 



Fig. 240. — Sporophyte of a club-moss (Lycopodium clavatnm). The horizontal stem 
is densely covered with leaves ; those OB the erect branch become small and few tor a 
space: these are succeeded by broader leaves, the sporophylls, crowded in a dense 
spike, s. Half natural size.— After I'rantl. 

Fig. 241. — Section through three sori of an aquatic femwort {Salvinia natans). 
Each is covered by a double indusium. r, /. two sori consisting of sporangia con- 
taining microspores <see tig. 242); <». a sorus consisting of sporangia, each containing 
one megaspore. M agnified 10 diain. After Sachs. 



which bear them, so that the microspores are said to produce 
male plants, and the megaspores female plants. For a fur- 
ther account of the gametophyte, see • 386, 394, 393. 

328. Seed plants. — In the seed plants this differentiation 
of the spores is always found. The microspores are called 



VEGE TA TI I r E REP ROD UCTION. 



235 



pollen, and the megaspores are called embryo-sacs * The mi- 
crosporangia and megasporangia, also, are always different in 
form and structure, and the leaves upon which they are usually 
borne are also of two distinct forms. In no case do sporo- 
phylls perform nutritive work; they are always specialized. 
Those leaves which bear microsporangia are called stamens^ 
and the leaves which produce the megasporangia are called 





Fig. 242. — A, a microsporangium of Salvinia seen from the outside. It contain?; (<^ 
microspores. />', four spores from A, surrounded by hardened frothy mucilage. C, 
median longitudinal section of a megasporangium, showing structure oj wall at matu- 
rity, and the single spherical megasporc, with its proper wall (black line) and a thick 
frothy epispore ill 368). A and C magnified 55 diam. B, magnified 250 diam.— After 
Strasburger. 

carpels* (figs. 245, 250, 251). In spite of these special 
names, it must be carefully borne in mind that the sporangia 
and sporophylls of the seed plants are not different from those 
of the fernworts or mossworts in any essential particular. 

329. The sporophylls of the seed plants are usually aggre- 
gated by the failure of the internodes of the axis to lengthen 
as much as between the foliage leaves. Very often, also, the 

* These special names were given because the seed plants were first 
studied, and it was long before the real nature of the pans and theii n la 
tion to similar ones in the lower plants were known. The terms are still 
in use, and are likely to continue to be used for convenient e. 



236 



PLANT LIFE. 



leaves adjacent are modified in form and color to adapt them 
to securing the dispersal of the pollen by various agents, 
especially insects. Such a shoot bearing sporophylls and 
accessory leaves is called a. flower (*\ 330). As a similar 
aggregation of the sporophylls occurs in horsetails and many 
club-mosses (figs. 235, 240), it is evident that the flower is 
not distinctive of the seed plants, though it attains the highest 
specialization among them.* 

The parts and functions of the flower of seed plants are 
now to be discussed. 



The Flower. 

330. A flower, in its simplest form, may consist of an axis 
bearing only a single sporophyll (fig. 243). A flower usually 
consists of a shortened axis, the torus, bearing several sporo- 
phylls and several accessory floral leaves (figs. 104, 244). 




Fie z 43 . 

Ho. -M3-— -'. a single flower ; /.', a portion of the flower cluster of A risarum r»/i,'<"''. 

The flower is composed of one stamen only. Magnified slightly.— After Kngler. 
Fir.. 244- A Mower of linden, halved; showing a pestle-like pistil. Magnified about 3 

diam. — After Reiner. 

The sporophylls arc known as essential organs, the accessory 
leaves as the perianth and bracts. 

The essential organs are of two sorts, stamens and carpels. 
In any flower they may be all stamens or all carpels, or may 

* It is for this reason that the term see J plants is preferred to Jlozuering 
plants. 



VEGETATIVE REPRODUCTION. 237 

include both sorts of sporophylls. The perianth may be com- 
posed of one or two kinds of Leaves, often bright-colored. If 

there are two sorts, those next the sporophylls are generally 
highly colored, and constitute the corolla. Each leaf of the 
corolla, when distinct, is a petal. The leaves below the co- 
rolla are often green. They constitute the calyx, and each, 
when distinct, is a sepal. 

331. Carpels. — The leaves (sporophylls) bearing the 
ovules (megasporangia) are called carpels. They ma\ In- 
flattened ; or so curved that in the course of their develop- 
ment the edges unite and a cavity is more or less perfectly 
enclosed; or neighboring carpels may grow together in such 
a way as to form a case. Such hollow structures, whether 
composed of one or more carpels, are often somewhat pestle- 
shaped, whence they early received the name pistil (fig. 244). 
A flower whose only essential organs are pistils is called pis- 
tillate. The sporangia arise usually upon the ventral (inner) 
face or the edges of the carpels. In the open carpel they are 
exposed, but in the closed carpels they are completely shut 
in, except for a narrow opening which sometimes remains, by 
which the interior cavity communicates with the outside air. 

332. Ovules. — Among seed plants the sporangia which the 
carpels bear are universally known as ovules, a name given to 
them under the supposition that they were the eggs which, 
upon fertilization, produce new plants. Though they are not 
in any respect comparable to the real eggs (since the) are 
produced by the non-sexual or sporophyte phase), the name 
is retained for convenience. 

333. Gymnosperms and angiosperms. — When the changes 
through which the ovule passes are complete, it bee nines the 
seed. When the ovules are produced upon the free stirfai e of 
an open carpel, the seeds are, therefore, exposed. On the 
contrary, when the ovules are borne within a closed pistil 
(formed by one or mure carpels) the seeds are developed 



2 3 8 



PLANT LIFE. 



within this case, by which they are protected until mature, or 
longer. 

These two methods of seed pioduction form the basis for 
the separation of the seed-bearing plants into two great groups, 
one known as gymnosperms, or plants with naked seeds, the 
other as the angiosperms, or plants with encased seeds. 
Open carpels are found exclusively among the gymnosperms, 
to which belong the cone- bearing, mostly evergreen, trees, 
while the closed pistils are chiefly found among angiosperms, 
to which belong the majority of garden and field plants and 
the deciduous forest trees. 

334. The simplest form of carpel occurs in Cycas (fig. 
245), in which the ovules are borne on the edges near the 
bases of leaves which somewhat resemble the foliage leaves, 
and form a whorl between preceding and succeeding whorls 
of foliage leaves upon the main axis. The carpel of most 
gymnosperms is a scale from 
whose upper surface arises a 
similar fleshy scale, the pla- 
centa, bearing two ovules 
upon its ventral (upper or in- 





FlG. 245. Fir.. 246. 

Fig. 245. — An ovule-bearing leaf or carpel of Cycas r*wfl/Kfa, showing 4 ovules near 
base, replacing the 1t.uu lies. ( hi the right above, a young seed. About one qu liter 
natural size.— After Sachs. 

Fk; 246 —A young cone-scale (placenta) of Scotch pine showing the two ovules; the 
latter halved parallel to the scale, showing the body of ovule and the prolonged integ- 
ument forming the micropyle, in. The scale is attached at /». Magnified about 8 
diam. After Kerner. 



VEGETA TIVE REP ROD I r C2 'ION. 



239 



ner) face (fig. 246). In such cases the carpels are generally 
aggregated in close spirals near the end of a thickish axis, 
and finally ripen into a cone (tigs. 341, 358), which gives 
the name to one of the largest orders of gymnosperms, the 




Fig. 247. — .-/, shoot <>f the yew ( lux us baccata) with three ripe seeds, each surrounded 
by a fleshy aril. Natural size. B, ovule with its tip projecting from the scale leaves 
dt the shoot it terminates. ( . the same, halved, showing the body of ovule (sporan- 
gium] and the lone; tube-like integument. O, young seed ol same, with aril partly 
formed. E, mature seed, halved. The central (white) body is the embryo; around 
it (dotted) the food ; then the seed coat; then the aril (white!. A', C, /'.A', slightly 
magnified. — After Kemer. 



Conifers. (See further ^| 404.) The ovules of some gym- 
nosperms are not borne by carpels, but each terminates an 
axis, as in the yew (fig. 247). 

335. The closed pistils of angiosperms are usually distin- 



240 



PLANT LIFE. 



guishable into (i) an enlarged basal part, the ovular?,* con- 
taining the ovules, surmounted by (2) a slender part of vari- 
able length, the style, which is terminated by (3) a rough, 
sticky, or branched part, the stigma. (See figs. 250, 258.) 

336. The stigma may take the form of a knob, a ridge, 
a straight or wavy line, or be lobed or branched. However 
compact, it is usually roughened by the prolongation of 
its surface cells into rounded, pointed, or hair-like exten- 
sions (figs. 248, 283), which frequently 
secrete a sticky fluid. Its purpose is 
to secure the adhesion of the pollen 
spores brought to it by various agents, 
among the most important of which are 
the wind and insects. 

337. The style may be thick or 
slender, long or short, branched or un- 
branched, hollow or solid. It is fre- 
quently wanting, so that the stigma is 
said to be sessile upon the ovulary. 

338. Simple and compound pistils. 
^fromV^gl*! com —When several carpels are present in 

to C Sch Z r£"&i f^'Cd! one flower the >' may form as many 
ZSL^&vFSaZ separate simple pistils as there are car- 
#ft&ffi£E-£ P<*s. ^ numerous, the axis will -be 
After straslurger. enlarged or elongated to accommodate 

them. (See ^[ 360.) Instead of forming separate pistils, 




* This part was early called the ovary (a name which is still in general 
use), meaning the organ which produces eggs, under the impression that 
the ovules ( = little eggs) were like the eggs of birds, an idea which was 
further carried out in the name albumen given to the fond stored in the 
seed. (See ' ,T 403, 407. ) To avoid confusion with the true ovary (1 388), 
in which the real egg is produced (^ 387), I here suggest the name ovu- 
lary — i.e., the organ which produces ovules. The word ovule, though as 
had in etymology as ovary, is convenient, and does not lead to any con- 
fusion. 



V EG ETA TIVE RE PROD UCTION. 



24I 



the carpels may be united to form a single compound pistil. 
This union is commonly brought about (1) by the actual 
growing together of the parts in a very young stage, so that 
the cells interlock and become partially or completely united; 
or (2) the carpels develop, not as separate- parts, but as a 
ring of tissue growing up from the surface of the axis; or, 
(3), a portion of each carpel develops separately, and later 
these distinct parts may be lifted by the growth of the ring 
of tissue beneath them (fig. 249). 

339. The union * of the carpels may be only at the base ; 
or it may involve the entire ovulary, leaving the styles free; 






Fig. 249. Fig. 250. Fir,. 251. 

Fig. 249. — Pistil of white hellebore (Veratrwn album) showing time carpels separate 

above only. Magnified about <• diam. After llerg and Schmidt. 
Fig. 250. — Calvx and pistil of the manna ash (Fraxinus ornus) showing calyx leaves 

united at base and carpels united throughout, the slightly 2-lobed stigma only giving 

external evidence of their number. Magnified several diam.— After Berg and Schmidt. 
Fig. 251.— Pistil of white potato halved transversely, showing two carpels united at 

center where their edges form ,1 large placenta on whose surface the ovules arise. 

Magnified several diam— After ICeraer. 

or the union may be complete, with the exception ot the 

stigmas, or it may involve even them (tig. 250). Union may 
take place in such a way that the edge of each carpel meets 
its fellow and the edges of neighboring carpels in the center 
of the compound pistil (fig. 251). In this case the ovulary 

* This phrase may It used for convenience in all cases, oven of those 

pistils in which the carpels were- at no time separate, 



24- 



PLANT LIFE. 



is divided into as many chambers as there are component 
carpels, and the partition by which the chambers are sepa- 
rated represents the adjacent parts of the two carpels. Or 
the carpels may unite with each other at their edges only, so 
-rr'sr-^^Tj^s, that the line of union is at the outside 
^^ s— cg^l ^^^ of the pistil. In this case the ovulary 
will have a single chamber. In both these 

FlG. 252. — A transverse . 

section of the capsule of methods of union the normal number of 

shepherd's purse. The , 

pistil consists ,,f two chambers in the ovulary may be increased 

carpels, at whose united 

edges two placenta: are by OlltglOWths from the Carpels them- 

formed carrying the 

ovules (now seeds). The selves, as in figure 252, where Jrom the 

partition from one pla- 
centa to the other is an united edges of the carpels a plate of tis- 

outgrowth (false parti- 
tion) and not part of the sue has grown out to meet a correspond- 

carpel. Magnified about 

6 diam.— After Bessey. ing one from the other side, so that what 
should be a one-chambered pistil has become two-chambered. 
(Compare also fig. 276.) Even simple pistils are subject to 
such subdivision of their interior (fig. 253). 




Fig. 253. Fig. 254. 

Fig. 253. — Lower half of the pistil of Astragalus canadensis. It consists oi only one 
carpel, but is divided into two chambers by a false partition, an outgrowth from the 
midrib of the leaf. Magnified several diam — Alter dray. 

Fig. 254— Two stages in the development of the ovule of the currant, ./.a median 
longitudinal section ol a young ovule; n, the sporangium; //.inner integument be- 
ginning to develop as .1 nng at base oi n ; .'/, the fundament of the outer integument ; 
»r, the mother cell of the niegaspores ; /,', a similar section of tin sporangium alone, 
older, showing »/', ;//", «/'", the daughter cells of m ; ///'". only becomes a perfect 
spore; m' and m 1 ' do not develop further and become destroyed. Contents of cells 
not shown. Magnified 350 diam. — After Warming. 

340. Ovules. — An ovule consists of a megasporangium 
partially enveloped by one or two outgrowths from beneath. 



VEGETATIVE REPRODUCTION. 243 

The sporangium forms the body of the ovule (fig. 254). In 
the interior the mother cells of the megaspores are differen- 
tiated early, the outer tissues forming the wall of the sporan- 
gium (fig. 254). In a few ovules as many as 20 to 40 mega- 
spores begin to develop ; in most only one to' four. Even 
when several megaspores begin to form it is rare for more 
than one to reach perfection ; the remainder disappear 
almost completely. 

341. Indehiscence. — The megaspore never escapes from 
the sporangium ; a condition which necessitates many adapta- 
tions. (See further « r 358, 414). The protection of the 
megaspore by the sporangium renders a thick wall unneces- 
sary. For this reason the megaspore looks more like a cavity 
in the ovule than like a spore. Because an embryo appears 
later inside this apparent cavity, the megaspore of seed plants 
has long been called the emhryo-sac. 

342. Integuments. — The sporangium is surrounded by 
one or two integuments. These arise as outgrowths from 

the tissues adjacent. If the spo- ^-^ w 

rangium is to have two coats, the *r* | L 

inner appears first as a low ring A, V /'/'■Jf""' I 

around its base gradually growing , ^"y 

up around it ; the outer shortly , ^^^ 

appears in the same way (fig. 255). 

_, . 11 1 Fig. 255.— Two very young ovules 

I hese integuments, as well as the of the California puppy ,/„/,. 

scholtzia I, seen from the outside. 
sporangium, often grow unsvm- /•'. somewhat older than 

. '. the sporangium ; fc, the inner in- 

metncally, so that at the maturity tegument; /■>■, the outer integu 

ment; ///, the -ulk. Magnified 
Of the megaspore the OVUle is Often [4odiam Mtei Duchartre. 

variously curved (figs. 254, 255, 256). The megaspore it- 
self may be distorted by this means so as to lose still more 
its likeness to a spore. 

343. Location. — Ovules are borne either upon the axis 
itself or upon the carpels. When they are borne upon 
the axis they may be either uncovered, as in the yew 



244 



PLANT LIFE. 



among gymnosperms (fig. 247), or the carpels* may form 
a covering, as in angiosperms. In these plants the ovule 
may terminate the axis, as in sunflower and buckwheat 
families (fig. 257); or the ovules may be lateral upon 
the surface of an enlargement of the axis within the ovulary, 
as in pinks and primroses (fig. 258). 

It is usual, however, for the ovules to arise upon a carpel, 
either singly or in clusters which occupy definite portions of 
its surface. The cushion or ridge from which the ovules 
arise is called the placenta. In the pines the placenta is a 




Fir;. 256. — Diagrams of median longitudinal sections of three sorts of ovules to show 
curvatures due to unsymmetric growth. A, a straight, />', an inverted, C, a bent ovule. 
In all: _/, the stalk; X-, the sporangium; //, the inner integument; at, the outer in- 
tegument ; m, the micropyle ; c, the base of the sporangium where the integuments 
arise (called the chalaza); r, the ridge (rhaphe) formed by the union of stalk and outer 
integument ; em, the megaspore. As C develops further em may become sharply bent 
on itself.— After l'rantl. 



scale-like outgrowth from the upper surface of the carpel, 
bearing two ovules (fig. 246), and as the cones mature these 
gradually outgrow the carpels and constitute the main por- 
tion of tlie ripened cone. To such placentas the ovules are 

attached by one side ; they are therefore entirely sessile. The 



•Although the enclosing leaves in this case do not bear the sporangia, 
and are, therefore, not strictly sporophylls, their similarity in form renders 
it convenient to retain the name carpel even for those pistils in which 
they are a mere roof over a convex or hollowed axis bearing the ovules. 
(See fig. 25S.) 



VEGETA TIVE REPRODUCTION. 



••15 



placenta in angiosperms commonly consists of a cushion of 
tissue usually at the united edges of the carpel or carpels, [f 
the carpels are united into a compound pistil, the placentas 
will be cither isolated, as ridges upon the inner face of the 
wall of the ovulary (fig. 25 2 J, 
or aggregated at its center 
(fig. 251). Occasionally the 
ovules arise upon the entire 
inner face of the carpels, as in 
the gentians. 





Fig. 257. 



Fig. 258. 



Fig. 257.— A median longitudinal section through the flower of Klu-um undulatutn, 
s, a sepal; /. a petal; n. a, n, anthers; «, stigma; /. ovulary; kk, sporangium, 
which, with the two integuments over it, forms the single ovule terminating the axis ; 
</>; nectary Magnified about 10 diam. — After Sachs. 

Fig. 258. -Pimpernel lAmtgnUu arvensis). A, median longitudinal section ol a 
young flower-bud ; /.sepal; c, corolla, just beginning to develop ; .(.anther; A", car- 
pels growing over A. tne apex ol the axis. />', median longitudinal section ol the 

pistil. . . the carpels, forming a root over S, the axis on which ovules are beginning 

to develop, and growing up to form a columnar style at whose apex is the stigma, '.. 
(', the same, older. ,S, the enlarged apex of the axis showing six ovules, Sk, in sec- 
tion; gr. the style: n, the stigma, on which arc lodged pollen grains, p. All magni- 
fied.— After Sachs. 



344. Stamens.— A stamen is a leaf (sporophyll) of the 
seed plants which bears the microsporangia, or pollen sacs. 
The flowers whose essential organs are all stamens are said to 



246 



PLANT LIFE. 



be staminate. Rarely a single stamen constitutes a flower. 
Except for the crowding, the stamens are arranged like all the 
other leaves of the plant, arising on the axis alternately, or 
in one or more circles. The stamens exhibit great diversity 
of form and size. Each usually consists of two parts, a stalk, 
called the filament, bearing an enlarged portion, called the 
anther. 

345. The filament may be long or short, slender or thick, 
rounded or flattened. It may be entirely wanting, in which 
case the anther is sessile. 

346. The anther is usually larger than the filament and 
commonly two-lobed, having the sporangia located in the 
thicker parts. The sterile tissue between the sporangia is 
called the connective (fig. 262). This appears usually as a 
mere continuation of the filament, but sometimes is prolonged 
beyond the body of the anther, as an appendage (fig. 259). 





Fig. 260. 

Fi<;. 259. — Anther of the sweet violet (Viola odor,tta), showing the connective pro- 
longed into a triangular tip. Magnified about 5 chain- After Knurr 

I ig - \ ut 1 1.1 of thyme ( Thytnui serpyllum), showing broad connective. Magni- 
fied about 5 diam. — After (Center, 

I'M.. 261. — Anther of the sage {Salvia <>/'//, inalis). Opposite a the filament proper is 
jointed to the elongated connective which has one perfect anther-lobe on the upper 
end; on the other the sporangia do not develop. Magnified about 5 diam.— After 
K, enter. 

It is sometimes broad, so that the sporangial lobes are widely 
separated (fig. 260), and may even be so long and slender as 
to seem a part of the filament (fig. 261). 



VEGE TA TIVE REP ROD UCTIOM. 



M7 



347. Sporangia.— The anther bears from 1-12 micro- 
sporangia upon its surface, or wholly or partly sunk in its 




Fig. 262.— Transverse section of the anther of thorn-apple (Datura Stramonium). 
c, connective, with a small stele embedded in parenchyma ; a, />, a, /, the four spo- 
rangia, arranged in pairs showing pollen grains. When the sporangia break, the walls 
rupture at the groove between a and /. Magnified about 25 diam. —After Frank. 



tissues. In most anthers the sporangia are either 2 or 4 

(fig. 262). When there are four they are often paired, and 

each pair may become confluent by 

the absorption of the portion of the 

anther tissue between them (fig. 263). 

This occurs about the same time that 

the outer wall bursts in order to set 

free the spores. Such anthers, at the 

time of opening, are apparently two- 

chambered. In those which contain 

only two sporangia, the two may open Fig. 263. -Trans verse section of 

. . bursted anther of a lily (Bu- 

independently, or they may become tomus umbeiiatus). Sporangia 

n , , have ruptured at z, so th.it the 

confluent, so that at maturity they two pairs have each formed a 

single cai itv. The coi 
may seem to constitute a single is relatively small; in the centei 

a single stele. Magnified about 
chamber. 2odiam. mm Sachs 

348. Dehiscence. — The opening of the 1 hambers occurs in 

one of three ways : by pores, by slits, or by valves. (1) A small 

area of the outer wall is absorbed or breaks away so that the 




2 4 8 



PLANT /.//■/■:. 



pollen spores sift out through the pore so formed (fig. 264) ; 
or (2) a crack begins at one point and extends lengthwise of 
the sporangium, in which case the anther is said to open by 
slits (figs. 259, 260, 261) ; or (3) the break occurs along a 
line considerably curved, and the flap (valve) thus loosened 
curls up or lifts so as to allow the escape of the spores (fig. 
265). All three methods are dependent upon some special 




Fig. 265. 



Fie. 264. — Anther and pollen of a Rhododendron. A, the anther, opening by pores at 
the end and allowing the pollen to escape. Magnified 8 diam. //.pollen grains ad- 
herent in four-, (tetrads) as formed in the mother tells: the tetrads an- held together by 
a stirkv material which draws nut i 1 1 1 . . cobwebby threads as they are separated. Mag- 
nified 50 diam. — After Kernel 

FlG. 205. A flower oi cinnamon, halved. The calyx and stamens are raised on a cup 
developed around the pistil. The anthers open bj uplifted valves, one for each spo- 
rangium, which lure are arranged in two stories instead of in pairs side by side. Mag- 

nilied about 7 diam. — After 1. 



structure of the wall of the sporangium at the lines of rup- 
ture. 

349. Union. — The stamens are not infrequently united 
with each other or with some of the neighboring leaves of 
the flower. They may l>e united to ea< h other by their fila- 



i "/•/<//•; ta ri i •/•; retrod uction. 



249 



merits only, or by their anthers only, or throughout their 

whole length. Union with the pistil or pistils is rather un- 
common, but union with the corolla or calyx is very frequent. 
The union of stamens may be real or apparent. They may 
develop independently anil later 
cohere by their adjacent edges 
(fig. 266). Or they may begin 
development separately and be 
subsequently raised by the growth 
of a ring of tissue of the torus 
(•[360), so that the free portions 
arise from the top of a shorter or 
longer tube. "When the stamens 
and corolla, arising independently, 
are carried up together by the 
growth of such a zone of the axis, 
the stamens appear to arise from 
the surface of the corolla (fig. 
267). 

350. Branching. — The sta- 
mens frequently branch, and this 
is difficult to distinguish from the 
displacement by basal growth just 
described, except by studying 
their development. When sta- 
mens branch a single fundament appears, on which later arise 
smaller knob-like elevations, the fundaments of the branches, 
each with its own growing point. (See figs. 268, 269, 270; 
also • 171 and figs. 146, 166 on branching of loaves, of 
which this is only a spe< ial case.) 

351. Pollen grains. — The microspores produced in the 
sporangia of the stamen are at maturity single cells. Their 
forms and walls are various, being round, ovoid, or even 

angular, with the surface smooth, grooved, or roughened, with 




sunflc 



The stamens of one of the 
family (Cosmos bi/>hi- 
natus). A, stamen tube formed by 
five stamens coherent by their an- 
thers around the style; the fila- 
ments with a tuft of hairs about the 
middle. />'. the same, but stamens 
only; the tube has been slit along 
one side and opened out Hat; seen 
from the inside, Connective pro- 
longed; dehiscence by slits Mag- 
nified about 7 diam. After Baillon. 



PLAiXT LIFE. 



few or many bosses, points, or ridges, as in other spores 
(A-D, fig. 271). In the pines the outer layer of the wall 



G'g-^s 




Kig 1*67. Fig. 269. 

Fig. 267. — Corolla of Alcanna tinctoria slit and laid open, showing almost sessile 
stamens united with corolla above the middle of tube, s, scale-like outgrowth from 
corolla. The tube between .v and the notches at edge of corolla result from the growth 
of a ring of tissue beneath the five fundaments of the corolla which produce the five 
corolla lobes c. Having grown so tar, a ring of tissue inside, on which the stamen fun- 
daments were developing, became involved in this upward growth, and thus the sta- 
mens were carried up and arise just above j. Magnified 4 diam. — After Berg and 
Schmidt. 

Fig. 268. -Very young flower of Hypericum perforatum, seen from above, showing 
s, sepals; /•, fundaments of petals ; a, a, a, fundaments of the three stamens, each al- 
ready with two lateral growing points, the fundaments of branches, appearing; g; fun- 
daments of 3 carpels. Compare with figs. 269 and 270. Magnified about 50 diam. — 
After Frank. 

Fig. 269, An older stage of fig, 268, showing only the fundaments of stamens, a, and 
of carpc-K. g: < in the- latter at the angles appear the fundaments of the three styles. 
Many branches of a have begun. Compare tig. 270. Magnified about 50 diam. 
— After Frank. 



forms two bladdery swellings which make the spore relatively 
lighter (E, fig. 271). The pollen spores arise in the spo- 
rangia in fours in each mother cell, as described in ^j 306. 
(See also fig. 264.) They are either dry and powdery when 



VEGETA TIVE REPRODUCTION. 



251 



ng to 



the sporangia burst, or are mois 

each other in larger or smaller 

clusters (fig. 264). Sometimes, 

as in orchids and milkweeds, they 

are all held together in one mass 

by the remnants of the mother 

cells in which they were formed, 

and are attached to a part of the 

tissue of the anther which carries 

the mass as a stalk or handle (figs. 

272, 273). Dry spores are usually FlG 

adapted to distribution by wind; fSSdtf-^lf^o? 

while the adherent spores are t^t^T^^t^. 

adapted to carriage by small ani- L%^ Fra M k agnified ab ° Ul 3 ***' 

mals, especially insects. (See further^]" 481.) 

352. Germination in place. — By the time the sporangia 




270. - Mature condition of the 






Fig. 271.— Pollen grains. A, white water lily (Nymf h ten alba). B, a thistle (Ctrswm 
>ii-mo>aU-). C.a mallow {Hibiscus ternatus). D, dandelion {Tat 
cinale). Magnified 200 diam.— After Kerner. E, pine, showing bladdery enlarge- 
ments, *,*,oi the outer layer of the cell-wall. The central portion is the body of the 

spore filled with protoplasm with a large nucleus. Kroin it is separated a lenticulai 
cell, /'. the rudiment ot tile gainetuphyte. Magnified 400 diam -Alter Strasburgei 



are old enough to release the spores, the latter have already 
germinated and begun to form a new sexual plant, the male 
gametophyte. Thus the spores of the non-sexual plant give 



252 



PLANT LIFE. 



rise to a plant of the other or sexual phase ; the sporophyte 
produces the gametophyte. (For a description of the plant 
thus formed see * 3 85.) 

353. Perianth. — The perianth is not present in any 





Fig. 272. — A, hanging flower of milkweed, seen from the side. The petals are sharply 
reflexed. Natural size. />, the upper part of same, magnified about 2} diam., with 
two of the appendages, ,/. ol the stamens cut off and the front of the anther wall dis- 
sected away to show its two pollen masses. C, two pollen masses from neighboring 
anthers connected to a dip, by which they may be attached to the foot of an insect. 
Magnified about S diam. /». foot of an insect with pollen masses attached. In (and 
D the pollen masses are inverted as compared with their position in . / and /•'. — After 
Kerner. 



gymnosperms (^[ 2,2,2,), except in a rudimentary form in a 
few species of the highest order. In angiosperms the 
perianth, which is rarely wanting, is primarily for the 
protection of the sporophylls. As in all cases where leaves 
are produced rapidly and in dose proximity on a short 
axis, they grow during their earl] Stages more rapidly 
upon the outer face than the inner. They are, therefore, 
concave inward and closely pressed together, forming a hud. 
At a certain stage the growth upon the two faces of the 



VEGETATIVE REPRODUCTION. 253 

perianth becomes equal, and later is more rapid upon the 

inner face than the outer. At this time Jt$$b> 

the flower unfolds, the perianth spreading Jf ^$$ 

more or less and exposing the stamens jpjr 

and pistils within. These variations in g ^^ ctl 

growth are often repeated, the stimulus ^fT 

being light or heat or both, when it is Fic.273 -Pollen massfrom 

,1 an orchid. The pollen 

necessary to protect the spores against gndns are arrang ed in 
unfavorable weather. Such flowers open legated at 7he C end r< of g a 

j 1 , . • \ c ii • 1 stalk, cd, terminating in 

and close several times before their leaves an enlarged sticky disk, 

. , /c , , w oei \ e.bymeansof which the 

wither. (See also % 286.) p() n en mass adheres to 

354. Calyx and corolla. — The leaves of ?^&?m.— Arur lngie°r Ut 
the perianth are usually arranged upon the torus in two or 
more circles or in a low spiral. They may be all alike or 
differentiated into two series, an outer and an inner. In the 
latter case those of the outer row or rows constitute the calyx, 
and the inner set the corolla. 

355. The calyx. — The calyx leaves, or sepals, are generally 
green and possess a great variety of form. When separate, 
the sepals are usually sessile and broad, with more or less 
pointed apex. The sepals are often apparently united in the 
manner already described for the stamens, the originally 
separate portions appearing as teeth or lobes at the rim of a 
cup or tube, or some similar structure. Occasionally the 
sepals are not persistent, but tall as the bud opens or shortly 
thereafter. More commonly, however, the calyx, especially 
when undivided, remains throughout the entire development 
of the flower, and often of the fruit. 

356. The corolla. — The inner set of perianth leaves, the 
petals, constitutes the corolla. The corolla presents a greater 
variety of form and color than does the calyx. The petals 
may be sessile or have a short or long stalk (fig. 274). The 
corolla ma) develop a cup or tube, as described tor the calyx, 
with teeth or lobes representing the petals (c, c, fig. 267). It 



'54 



PLANT LIFE. 




may be lifted on a common tube with the calyx from which 
it then seems to arise ; or it may be raised 
with the stamens, which then seem to be 
attached to it, as in figure 267 ; or stamens, 
corolla, and calyx may be lifted together 
(figs. 288, 355). The corolla is ordinarily 
not persistent, usually falling or withering 
shortly after the microspores have been 
lodged upon the stigma. 

357. Irregularity. — Both corolla and 
ig. 274.— Outline of a calyx are often radiallv symmetrical — i. e., 

petal of Lychnis, 

showing long stalk the parts surrounding the center of the 

and an outgrowth, n, 1 

the Hguie. Compare stem are of equal size and like shape, 

fjpr rM Aftpr T .nprQ- 

scn 



37. — After Luers- 



md may be divided into several like halves 
by radial planes (figs. 275, 276). But often the symmetry 
of the calyx, and still more frequently that of the corolla, 




Fig. 275. 




Fig 276. 



Fir.. 275. — A flower of the flax, halved ; showing radial symmetry. See fig. 276. Magni- 
fied 2 diam— After liessey. 

FlG. 2-(k — Diagram showing the arrangement of the parts of a flower of flax. Outer 
circle, 5 sepals ; second, 5 petals; third, 5 stamens; fourth, 5 carpels, each divided by a 
false partition into 2 chambers. Five different radial planes will, therefore, divide this 
flower into halves.— After Bessey. 



is so altered by unequal growth of the parts that the flower 
can be divided into like halves by only one, or at most two, 



VEGE TA TI I r E KEPKOD UCTION. 



255 



planes; or it may even be entirely unsymmetrical. This 
unlikeness in the size and shape of the accessory leaves not 
infrequently extends to the sporophylls (figs. 277, 278). 

The irregular form and color of the perianth (when other 
than green), including the variegation of the ground color 
by lines and spots, seem to be dependent upon the relation of 
the flower to insects. (See further ^[ 484. ) 





Fig. 277. — An unopened Sower of tlie sweet pea, halved ; showing bilateral symmetry 

(irregularity. Slightly enlarged.— After Hessey. 
FlG. 278. — Diagram showing the arrangement of the parts of the flower of sweet pea. 

Outer circle, calyx >5-lobed> ; second, 5 petals, the two lower united; third, 10 stamens, 

9 united by filaments, 1 separate ; center, one carpel. Only one plane will divide this 

flower into halves. — After l'.essey. 

358. Pollination. — Since the megaspore is enclosed per- 
manently by the ovule, and in angiosperms the ovules are 
again enclosed by the pistil, it is necessary that the male plant 
growing from the pollen spores be developed in the neighbor- 
hood of the ovule whose megaspore produces a female plant. 
(See ^jl" 341, 3S6.) To insure this a portion of the pistil 
forms a receptive surface, the stigma, upon which the pollen 
spores may be readily lodged. It is advantageous, also, to 
have the pollen spores of one flower lodged upon the stigma 
in another flower of the same sort rather than upon the 
stigma of the same flower. The process of lodgment of 
pollen on a stigma is (ailed pollination. If the pollen from 
one flower is tarried to the pistil of another, it is tailed 
cross-pollination. * To secure pollination, and espei iallv 

* Since fertilization of the egg i- tin- ultimate object of pollination and 



256 



FLA. XT LIFE. 



cross-pollination, the agency of wind or water or insects is 

employed. To the peculiarities of these various agents, 
flowers adapt themselves in character of pollen, color, nectar, 
odor, form of parts, time of development of stamens and 
stigma, etc. For an account of these see € • 477-482. 
359. Bracts. — In the immediate neighborhood of the 
perianth the leaves are usually modi- 
fied at least in form and size, and 
not infrequently in color. The 
leaves in whose axils the flowers 
arise are called bracts, as are also 
those which subtend branches of the 
inflorescence (//', //", // 3 , fig. 139). 
The axis of the flower, when 
elongated beneath it, usually bears 
one or more bractlets. 

The bract is sometimes large and 
surrounds the entire inflorescence, 
as in Indian turnip (fig. 279) and 
the calla, when it may be vari- 
ously colored. Highly colored 
bracts occur in the scarlet sage 

Fig. 279.— Inflorescence of Indian and, with incOHSpicUOUS flowers, 
turnip (.1 s/uuiia), surrounded 

by a large striped and mottled in poinsettia and painted cup, 

bract, the spatke. Natural size. 

—After Gray. while the four large whitish bracts 

of dogwood are the only conspicuous part of the inflores- 
cence (fig. 280). 

Bracts are aggregated to form an involucre beneath a head 
(T 104), as in the sunflower family (figs. 2S1, 409), or an 
umbel (^[ 104), as in the parsnip. The perianth may be 
almost or quite wanting, and the bracts and bractlets may 
be the only protective leaves for the sporophylls, as in the 

generally its final result, the terms close- or self-fertilization and cross- 
fertilization were formerly used. The word pollination is preferable. 




VEGETATIVE REPRODUCTION. 2$y 




Fig. 280. — Inflorescence of the dogwood (Cor nits florida\ showing four white bracts 
below- it, giving the whole cluster the aspect of a single (lower. Two thirds natural 
size.— After Baillon. 




Fig. 281.— Inflorescence oi yarrow {Achillea millefolium). A, seen from above; /■', 
in longitudinal Bection. r, bracts, forming the involucre ; d, bra< 1- in whose axils the 
flowers stand; ra, the ray flowers; »//, the disk flowers; .. corolla; '.ovulary; 1, 
stigmas; >, the common torus. A magnified about 8 diam. ; B, about 15 diam Vftei 



2 5 8 



PLANT LIFE. 



grasses (fig. 282). Bracelets sometimes form a sort of second 
calyx beneath the true calyx, as in hollyhock. In the straw- 
berry and its kin, the somewhat similar extra whorl of leaves 




Fig. 282. 



Fig. 283. 



Fig. 284. 



Fig. 282. — A single flower of wheat, showing two chaffy bracts, />, v, which protect it. 
For the parts of the flower see fig. 2S3. Magnified about 5 diam. — After Luerssen. 

Fig. 283. — The flower of wheat with bracts removed, showing two fleshy bractlets, c, c, 
the lodicules, which at time of blossoming swell and open the bracts. Three stamens, 
and a carpel with two styles and feathery stigmas constitute the flower proper. Magni- 
fied about 5 diam. — After Luerssen. 

Fig. 284. — Outline of the flower of strawberry, seen from beneath, c, corolla ; k, calyx; 
k', epicalyx, formed by the union of the stipules of the sepals. Slightly reduced. — 
After Luerssen. 



belongs to the calyx, being the stipules of the calyx leaves 
united in the course of development (fig. 284). 

The " cup " of the acorn, the "shuck " of the beechnut, 
and the "bur" of the chestnut represent late-developed out- 
growths beneath the flower or the flower cluster, which be- 
come scaly or spiny as the nut develops, and serve to protect 
the forming fruits. 

360. The torus. — In the vicinity of the flower leaves the 
internodes of the stem are rarely developed, so that the nodes 
from which the flower leaves arise are close together. More- 
over, the axis is usually enlarged, so as to give greater space 
for the numerous leaves. This enlarged portion is called the 
receptacle or torus. When the leaves are removed or fall 
naturally the torus shows ordinarily a rounded or conical sur- 
face, with close-set scars left by their bases (fig. 285). When 



I 'EGE TA TI I '£ REP ROD UCTION. 



259 



a great number of sporophylls are to be borne, the torus is 
elongated, as in the mousetail (fig. 286); or greatly enlarged, 




Fig. 285. Fig. 286. 

Fig. 2S5— The torus of a flower of stonecrop (Sedum tematum), with the leaves re- 
moved to show scars ; two leaves of each kind shown a, sepal ; />, petal ; c, stamen ; 
ii, carpel. Magnified several diam. — After Gray. 

Fig, 286.— Flower of mousetail {Afyosurus mittimus), halved; showing s, spurred 
sepal : st, stamen ; st' , a staminode or sterile stamen, having the position and form of 
a petal ; t, elongated torus covered with carpels, some of which are cut through. Mag- 
nified several diam— After Engler. 




FlG. 2S7.— Flower of the strawberry, halved; showing elongated and thickened torus. 
Magnified about 3 diam.- After Bessey, 



as in the strawberry (fig. 287); or transformed into ;i cup, as 
in the rose (fig. 288). 

When flowers in large numbers nre very closely associated, 



!6o 



PLANT LIFE. 



as in a head (• 104). the receptacles arc joined to form a 
large common receptacle, as in the sunflower and its allies 
(fig. 281). The receptacle in such plants may he a cone, 
a dome (fig. 409), or a more or less flattened disk. In the 





Fig. 288. Fig. 289. 

Fig. 288. — Flower of sweetbrier rose, halved; showing urn-shaped torus. Compare fig. 

139. Natural size. — Attn- Bessey. 
I ■ , Tin- inflorescence of fig. halved lengthwise; showing common torus on 

whose interior surface many flowers are formed. Two fig wasps are near the opening 
of the flower chamber, one outside, while the other has just crawled in among the 
flowers. Natural size. — After Kerner. 

fig the common receptacle is pear-shaped, with the edges 
almost meeting above and the flowers distributed over the 
inner face of the fleshy sac (fig. 289). 



III. Brood buds, etc. 

361. Definition. — Single-celled spores pass without any 
sharp distinction into the multicellular bodies known as brood 
buds. For convenience, however, brood buds maybe de- 
fined as multicellular (sometimes unicellular) bodies capable 

of producing a new plant of the same phase as that from 
which they arise. Since this is a distinction for conve- 
nience merely, it is not desirable to distinguish brood buds 



VEGETATIVE REPRODUCTION. 26l 

from spores until the mossworts are reached, in which the 
alternation of phase is well marked. In their simplest form 
such buds consist of a single cell, though more commonly 
they are two- to several-celled. Some or all of their cells are 
in the embryonic stage (^] 256). Like spores, they are sup- 
plied with reserve food. 

362. Simple forms. — The form of brood buds is various. 
When not differentiated into distinct organs, they are club- 
shaped, lenticular, or spherical. In some thalloid liverworts 
(Marchantia and Lunularid) they are produced on the surface 
of the thallus, surrounded wholly or on one side by an out- 
growth from the surface forming a cup or a crescentic ledge 
(figs. 59, 290, 291). In some mosses brood buds arise from 




Fig. 290. — Thallus of Marchantia, seen from above, showing the cups containing brood 
buds. See fig. 291. Natural size. — Alter Kerner. 



the apex of the stem, either in cup-like clusters of leaves or 
exposed (A,A f , fig. 292); in others they are smaller and 
simpler and are developed upon the leaves (B, B\ fig. 292). 
In all the mossworts they belong to the gametophyte. 

363. Shoots. — In femwortS and seed plants the brood buds 
belong to the sporophyte. In the latter they are espe< iallj 
abundant, and often reach considerable size ami complexity 
before being separated from the parent, usually consisting of 
a short axis with a growing point and at least rudimentary 



262 



PLANT LIFE. 




91. Fin. 2152. 

the development of a brood bud of Marchantia ; 



ill seen from 



Fig. 

Fig. 291. — Six stages 
side. I, very young 

older, terminal cell divided trans- 
versely. Ill, IV, V, successively older stages. VI. mature, cells not shown: two 
growing points localized on right and left edges. I-V, magnified about 250 diam.; 
VI, about 25 diam. — After Sachs. 

Fig. 292. — Brood buds of mosses. A , upper part of the stem of Aulacomnium audio- 
gynu m . with a cluster of brood buds at apex (magnified about 8 diam.), one of which is 
enlarged 120 diam. in A', />', tip of leaf of Syrrkopodon sender (magnified about i" 
diam.) showing brood buds ; />", some more enlarged labout 40 diam.). — After Kerner. 




Fig. 293. — Young plants developing from adventitious buds on leaves of a fern (Aspic 
vhich they readily separate to form 



muni i>ulbi/,-r iiniK from ■ 
size. />', magnified 2 diam. 



plants. A, natural 



VEGETA TIVE RETROD L'CTION. 



263 



leaves. They generally arise upon the stem, more 

from the leaves or the root. Upon 

the stem they usually take the place of 

shoots of other forms, developing from 

axillary buds (figs. 294, 296). If 

formed on leaf or root it is always from 

adventitious buds (fig. 293). 

Every possible gradation exists, from 
the simplest to those with well-de- 
veloped members, constituting a plant 
of some size. They may be artificially 
grouped as follows : 

364. {a) Buds. — In these the axis 
is short and the leaves scale-like. When 
most highly developed the quantity of 
reserve food is considerable and the 



rarely 




Fig. 294. — Fleshy buds in axils 
of the leaves of a lily (I. ili- 
um bulbi/eruiti). Some- 
what reduced. — After Van 
Tieghem. 




.y^ 



v\/f 



t. 






3M : 



jL_I- 



1 



Fig. 295.— Pond weed iPolamogeton crispus). Detachment o) spe< i.il shoots, hibenuu - 

ula, which are to hibernate under water. The plant ./ has one oi these shoots at the 
tip; B lias just loosened one, /;, which is sinking to the bottom. Two thirds natural 
size.— After Kemer. 



264 



PLANT LIFE. 




parts of the bud are often distorted 
by the enlargement of the tissues 
to contain the food. The fleshy 
buds which readily separate from 
the axils of the leaves of some 
garden lilies (fig. 294), and those 
which replace the flowers in some 
cultivated onions, are well known. 
(Compare also fig. 106.) 

365. (/') Hibernacula. — Some- 
what similar but more highly de- 



Fig. 296.— A plant of stonecrop [Sedum dasyfihyllum). Offsets are produced near the 
base on short brandies o, o ; at the tip of longer branches, o' ; and in place of the flow- 
ers, o". Natural size.— After Kerner. 




Fig. 297.— Formation of runners in the strawberry. ,t, the mother plant ; b, voung plant 
formed at tip of first runner; c, plantlet at tip of second ; a third has put out from c. 
Slightly reduced.— After Seubert. 



VEGET. I I'l I E RETROD UCTION. 



265 



veloped brood buds are formed at the approach of winter 
about the base of the stem in many perennials with her- 
baceous tops. These are separated by the death of the parent 
stem and produce new plants 
in the spring. Some aquatics 
show a similar habit, dropping 
short shoots to the bottom of 
the water in autumn, which 
are to grow in the spring (fig. 

295)- 

366. (r) Offsets, etc. — 
Some plants produce special 
branches, either underground 
or aerial, which develop at 
their extremities new plants or 
special structures for their for- 
mation. The housedeek or live- 
forever (fig. 369) and stonecrop 
(fig. 296) reproduce themselves 
by offsets. These are short 
branches with a rosette of 
leaves at the tip which is read- 
ily detached and rolls away, 
to take root at the first oppor- 
tunity and establish a new 

plant. The Strawberry and Fig. 298.— A plant of eel-grass (Vallisne- 

ria spiralis) forming new plants, a, b, at 

eel-gl'aSS form long leafleSS tips of runners, arising from axils of lower 
leaves. One third natural size. \tu-r 

branches which take root at the Schnizlein. 

tip and produce new plants, the slender runner subsequently 
perishing (figs. 297. 298). The white potato forms at the 
end of slender underground branches elongated tubers upon 
which are numerous buds, any one of which, nourished by 
the reserve food in the tuber, may produce a new shoot. 
The slender stem by which the tuber is connected with 




266 



PLANT LIFE 



the main axis perishes at the end of the growing season 
(fig. 299). 

367. (d) Cuttings or scions.— Closely related to this 
mode of reproduction is that by the separation of fleshy 




Fig. 299. — A seedling potato plant. ( is the baseoi the stum, below whi< h is the primary 
root. r. The primary leaves < t, are still present. The early leaves,./! rlre not so much 
branched as later ones will In-. In the axils of the lower leaves arise the branchi 
with scale leaves, e'e, and secondary roots, 1 . The tips of these branches, when 
illuminated, bear foliage leaves, /' ; but usually they thicken into tubers,//., which 
have scale leaves, e'i , in whose axil bud an formed, the o-called " eyes " of 

the tul hi Natural size. — After Duchartre. 

members, upon which are subsequently developed adventi- 
tious buds, which give rise to new plants. The thick leaves 
of Bryophyllum are often Mown off by storms, and produce 

new plants from buds formed at the teeth along the edge. 



I 'EGE TA Tl I £ RETROD UCTION. 



267 



Some species of Kleinia, natives of Cape Colony, have fleshy 
Stems, jointed at intervals, so that they easily break there. 
When broken off by an accident, the piece rolls away, takes 
root from the under side, and sends up shoots from the upper. 

Advantage is taken of this power of severed parts to form 
adventitious roots and shoots in the artificial propagation of 
domestic plants. Suitable portions of shoots or leaves for 
the development of new plants under proper conditions are 
called cuttings, scions, or "buds." They may generally be 
grown in water or soil ; or they may be securely fastened in 
a slit or wound in another plant. The latter process is 
known as grafting or budding, according to the form of the 
implanted part. Indeed brood buds in general may be 
looked upon as natural cuttings or scions. 

368. Branching. — A further modification of this method 
of reproduction is to be 
served in the formation 
new individuals through pro- 
gressive death of the older 
parts. If a plant, dying thus, 
be a branching one, death will 
sever the branches as it reaches 
them sooner or later, and 
each branch then becomes an 
independent plant. This is 
seen in its simplest form in 
those plants which have a hori- 
zontal branching thallus whose p 
base dies as the apex elongates Fig. 300.— Outline of a thaiius of u„>- 

\ 1 • • chant ia geminata. The base D is 

(fig. 300). It IS common in dying as the apices are growing and 

branching. Wheti death reaches the 
plants with underground Creep- first fork there will be two independent 

plants; at the second there will be four, 

mg* stems which send up aerial andsoon. 

leaves or shoots annually, as do the ferns of temperate regions 

and main glasses and mints. 




CHAPTER XVIII. 

SEXUAL REPRODUCTION. 

369. Cell union. — All methods of sexual reproduction 
consist in the formation of a single cell by the union of two 
specialized cells, known, respectively, as the male gamete and 
the female gamete. The essential step in their union is the 
coalescence of the nuclei. The cell thus formed is capable 
of developing into a new plant under suitable conditions, 
and is, consequently, a spore. Such sexually produced spores 
must not be confounded with non-sexual spores (see ^[ 304). 

370. Origin. — It is scarcely to be doubted that the earliest 
methods of reproduction were vegetative, and that sexuality 
has been acquired by a gradual modification of cells previ- 
ously devoted wholly to ordinary processes of growth. The 
probable history of the origin of sexual cells and sex organs 
can onlv be inferred from the fact that the simplest plants 
show no sexuality, others show imperfect sexuality, and still 
others complete sexuality. The data are very imperfect, but 
they enable us to form at least an intelligent idea of how 
sexuality may have been acquired. 



Theory of sexuality. 

371. Rejuvenescence. — Among the processes of growth 
in the simpler plants, especially the fission-algne (^[ 11), one 
of the most striking is that known as rejuvenescence. In this 
process the protoplasm of the cell escapes from the cell-wall, 
and acquires special motor organs known as cilia, which en- 

268 



SEXUAL REPRODUCTION. 269 

able it to swim rapidly, but apparently aimlessly, through the 
water. In this form it is essentially a zoospore. (See ^ 306.) 
After having moved about for a variable time and perhaps 
increased its volume by growth, it loses its cilia, surrounds 
itself again with a cell-wall, and resumes its ordinary mode of 
life. In filaments of some multicellular algae a similar process 
occurs. The contents of any cell may escape by the solution 
of the cell-wall and become a zoospore. After swimming 
about for a time the zoospore may come to rest, secrete a 
cell-wall, and by repeated divisions in one plane produce an 
individual similar to the parent. (See ^| 24.) It is evident 
that such a method would give rise economically to a con- 
siderable number of individuals. The process is essentially 
the separation of the filament into pieces, each being the 
contents of a single cell. 

372. Conjugation. — In other filamentous algae the cell- 
contents, instead of escaping as a single zoospore, divide into 
two or more zoospores. If, while these are still active, two 
accidentally collide, the possibility of their adherence and 
and the fusion of the two into one is conceivable. Such 
fusion actually occurs among the zoospores of alga;, and is 
(ailed conjugation, but in observed cases it follows a definite 
method, and is not merely accidental. It is probable, how- 
ever, that the first occurrence of conjugation was accidental, 
and that it has become fixed and definite because those indi- 
viduals in which it occurred with most certainty and regular- 
ity thereby produced the most vigorous offspring. 

373. Imperfect sexuality. — In the alga Ulothrix, we have 
a plant in which many of the processes just described still 
occur. It produces zoospores of two kinds: (1) large ones, 
with four cilia (C, fig. 301), formed in pairs in each cell (B) ; 
(2) small ones, having two (rarely four) cilia, and arising 
eight or sixteen from each mother cell (D). Both these sorts 
of zoospores will grow, after a period of swimming, into new 



270 



PLANT LIFE. 



plants, though the small ones produce very slender, weak fila- 
ments (fig. 302). Beside the zoospores, Ulothrix produces, 
under certain conditions, gametes, which are precisely like 




Fir,. 301. — Ulothrix zonata. .1, a young filament with rhizoid cell, r, at base. B, bit 
of a filament from whose cells large zoospores are escaping through a pore in the side- 
wall. C, a single large zoospore. D, bit of a filament from whose cells small zoo- 
spores lor gametes 1 are esi aping / ■', small zoospores lor gametes . /•', gametes con- 
jugating, (r, same, conjugation complete. //. zygote, before formation of wall to 
become a resting spore. Magnified 4S2 diam. — After Dodel-Port. 

the small zoospores in appearance. But their behavior is 
different. They usually conjugate freely in pairs and produce 
resting spores. If, however, they do not conjugate, each 



SEXUAL REPRODUCTION. 



2 7 I 



may round itself off and, alone, become a resting spore. 
These resting spores, after a dormant period, germinate and 
develop into new plants. 

In llothrix, therefore, the gametes are imperfectly sexual. 
Failing to conjugate, as many do, they may still develop into 
new individuals. A con- 
sideration of the appearance 
and behavior of the gametes 
leaves little doubt that they 
are merely small zoospores 
which have acquired imper- 
fectly the habit of conjuga- 
tion and retained partially 
the power of independent 
growth. 

374. Further develop- 
ment. — -The perfecting of 
reproductive methods fol- 
lowed the two lines just sug- 
gested. On the one hand, 
complete sexuality was ac- 

Fir.. 302.— Sporelings of Ulothrix zon.it*. 
quired by certain Cells, while a, a young plant from a large zoospore. 

/>, young plants from small zoospores which 
Others Were more Completely germinated without leaving the mother cell. 

Magnified 4S2 diam.— After Dodel-Port. 

specialized as non-sexual re- 
productive bodies. The latter have already been discussed 

(T3°4ff-)- 

Tracing now only the line of sexual development, it is 
probable that the first step in this differentiation was the 
failure of some of the zoospores to escape from the cell pro- 
ducing them. From this point two lines of development 
diverge. 

375. 1. Isogamy. — Along one of these lines, the zoo- 
spores ceased to form cilia, and became non motile sex 
cells, in some cases similar in form and function, and in others 




272 



PLANT LIFE 



like 



in form but unlike in behavior. This leads to the com- 
pletest form of conjugation, as seen 
in Mesocarpus, Spirogyra, and other 
Conjugate. (See *[ 25.) In these 
the contents of one cell of a filament 
enter those of another either by a 
partial solution of the partition-wall 
between them or by the formation of 
a tube-like outgrowth from one or 
both of the cells concerned, so that 
when these tubes come in contact and 
have their ends absorbed the contents 
of one cell passes over into that of 
the other (fig. 303). The cells con- 
jugating in this way may he either 
neighboring cells of the same fila- 
ment or cells of different filaments 
brought into proximity by acccident. 

Fig. 303 —Conjugation of .S> iro- , 

gymquinina. The cells a, a' In the course of development in this 

are just forming the conjugat- . . , . 

ing tube; the contents not yet direction conjugation reaches its 
fully reorganized as gametes. _ i ■ i 

The body protoplasm is not highest perfection, being secured with 

shown in these two cells, ... . , . 

though it is in the others such certainty that non-sexual methods 

(compare fig. 25, of another . 

species of Spirogyra). The are almost entirelv abandoned. 

cells b, b' have completed the «.„„_,, „, 

tube ; the ends have been dis- 376. 2. Heterogamy. — i he second 

solved and the contents of b 

is passing over into b' . This lj ne of development Was followed In- 
process is nearly completed in 

cells c, c'. 2, 2, zygotes, with other algae, and the method proved so 

protecting wall, thereby pre- ... , - 

paredto become resting spores, efficient that it became the dominant 

Magnified 150 diam. — After 

Strasburger. one in the plant kingdom. Among 

these algre there occurred a differentiation of the zoospores. 
The first step in this differentiation was an increase in size 
of one of the sex cells, so that they differed both in action 
and in form. To distinguish one from the other the larger 
sex cell is called the female cell, or egg, and the smaller, the 
male cell, or sperm. A further difference arose in the com- 




SEXUAL REPRODUCTION. 



273 



plete loss of motility by the female cell (fig. 304). When 
these differences exist in the sex cells their union is no 
longer called conjugation, but fertilization, the active male 
cell being said to fertilize the quiescent female ( ell. 

377. Sex organs. — A further stage in the development of 
sexuality is reached when the cells producing the sperms or 



Fig 
carpus. /■. sperm 




Differentiation of gametes in some marine algae 
lost 

1. ./. 1 
the extreme "I difference in she in gametes. All magnified equally (about 700 diam.), 



egg of Za 

before fertilization which is about to occur in (/ 



ke gametes of Keto- 
ne egg loses its cilia and rounds itself 
. sperm, _/. egg of incus. This is 



the eggs are differentiated. The cell or the Organ producing 
the egg has been known by various names in different groups 
of plants. An appropriate general name for it, without refer- 
ence to its structure, is the ovary. (See further* 335.) 



274 PLANT LIFE. 

The male organ was called the antheridium, from the idea 
that it was like the anther of seed-plants, which was once 
supposed to be the male organ of the flower. There is no 
special objection to the name, but a more appropriate one for 
it is the spermary, since these male cells are known as the 
spermatozoids or, briefly, the sperms. 

The final step in the development of sexuality is the restric- 
tion of the formation of sex organs to a certain phase in the 
life history of the plant, which is therefore known as the 
sexual phase, or gametophyte, the remaining phase or phases 
being called, for the sake of distinction, non-sexual, and con- 
stituting the sporophyte. The gametophyte alternates with 
the sporophyte, giving rise to the phenomenon known as the 
"alternation of generations." (See % 55.) 

378. Directive agents. — To secure the union of the male 
and female cells, the male gamete must be directed to the 
female. By what means this is accomplished is not fully 
known. Organic acids and sugar exercise such an influence 
on certain sperms that they swim towards the source of these 
substances. The wide distribution of such compounds sug- 
gests that probably their presence in the female gamete may 
render it attractive. W this is true, the sperms exhibit a spe- 
cial irritability towards these materials, whose diffusion acts 
as a stimulus. 

Isogamy. 

Sexual reproduction, as developed among existing plants, 
shows two main types, known as isogamy and heterogamy. 

379. Isogamy is thai mode of sexual union in which the 
size and form of the gametes is alike. In some cases the 
behavior also of both male and female isalike, while in others 
the male shows a greater power of movement. When both 
are equally motile and escape from the cell, conjugation occurs 
wherever they happen to come in contact. The form is usually 



SEX i A L KEF ROD UCTION. 



?75 




pear-like {E, fig. 301). The protoplasm at the narrower end 
is more transparent and hears two or more 
cilia ; while the larger end is occupied hy 
the reserve food and particularly the chloro- 
plasts, if present. Union of free motile 
gametes occurs by gradual coalescence, be- 
ginning at the pointed, transparent end {F, 
fig. 301). When the conjugation is com- 
plete the resulting spore (zygote) usually 
acquires a spherical form, soon secretes about 
itself a wall, and either begins to grow at 
once into a new plant or thickens the wall 
and becomes dormant for a time as a resting 
spore. In other cases the form of the 
gametes is determined only by the shape of 
the cell, from which they do not escape. The 
entire cell contents constitutes the gamete 
(figs. 303, 304). In such plants both 
gametes may be equally motile and meet 
in a branch, the conjugating tube, to form a 
spore, as in Mesocarpus (fig. 304) ; or the 
male gamete may be motile and migrate from the cell in 
which it is produced, through the conjugating tube into the 
cell containing the female gamete, with which it fuses, as in 
Spirogyra (l^. 303). 

The spore thus formed may be a resting spore, in which 
case it secretes about itself a thick wall, and remains dormant 
for several weeks or months. In the plants just referred to, 
the spores, funned in early summer, with the remnants of the 
parent cell-walls about them, sink to the bottom of the water, 
and do not germinate till the next spring. 



Fig. 305. — Conjugation 
of Mesocarpus. The 
contents of the two 
upper cells are accu- 
mulating in the con- 
jugating tube to form 
a zygote, which is 
complete in the 
lower tube. Magni- 
fied about 150 diam. 
— After DeHary. 



276 



FLAX J- LIFE. 



Heterogamy. 

Heterogamy is that mode of sexual union in which the sex 
cells are unlike, being differentiated into sperms and eggs. 

380. The sperms. — The body of the sperm is the cell 
nucleus, surrounded by a small amount of protoplasm which is 
often extended into one or more cilia (fig. 306). The more 
complete the differentiation of the sperm the smaller, as a 
rule, is the amount of body protoplasm. Whether or not the 
sperm is motile depends upon the conditions to which it has 
become adapted. Whenever motile, fertilization must occur 
in the presence of water of amount sufficient to permit the 
sperm to swim to the egg. 




Fig. 306. — Sperms of various plants, showing variety of form, t, Volvox aureus; 
1, Vaucheria synandra . ;, Ckarafragilis ; 4, Fucus serratus ; 5, Marchantia 
7, Marsilia vestita. Magnified kk»i 



polymorpha : 6, Equisetum Telmatei 
diam. — After Mbbius 



The spermary may produce only one sperm (fig. 307), or 
its contents may divide into many (fig. 310). When single, 



SEX I A 1 REPROD UCT10N 



2/7 



the form of the sperm is usually that of the cell in which it 
is produced. U it is set free, it may become globular, and 
have slow amoeboid movements, or it may be entirely im- 
motile. In the latter case it must depend upon the move- 
ments of the water into which it escapes for transference to 
the vicinity of the egg. The sperm may be ovoid and fur- 
nished at the end with one or more cilia ; or elongated and 
bent or coiled one or more times. The elongated forms 
have almost invariably two to many cilia (fig. 306). 

381. The spermary. — The organ in which the sperms are 
produced is the spermary or antheridium. It is either simple 
or compound. A simple spermary consists of a single cell 
whose contents is transformed into one or more sperms. 
Simple spermaries occur only in algae and fungi, and by 
reduction among seed- plants. (See ^[ 
3S5.) If more than one sperm is to be 
formed, the nucleus, originally single, 
becomes divided into as many parts as 
there are to be sperms (sometimes into 
more than become mature). The total 
number of sperms produced by a plant is 
related somewhat to the number of eggs, 
but particularly to the chances of the 
sperms reaching the egg. 

If there is but a 




Fig. 307.- The sex organs 

ingle sperm iormeu of Peronospora. /;, 

' hvplia which has devel- 

bv each spermary, either the number ot oped at the end the 

spermaries is great or some adaptation 

exists for the certain transfer of the sperm 

to the e^g. In Cystopus and its allies, 

for instance, a branch of the spermary 

grows into the ovary, through which the 

sperm passes to the egg (fig. 307). 

A simple spermary arises either by the 



egg (the centra] 
dark sphere <'.■'. hypha 
which lias developed the 

spermary. >:. who 
toplasm, constituting .1 
single sperm, is passing 
through the fertilizing 
tube (a branch ol the 

Magnified $50 diam 
Aftei DeBary. 

differentiation of 



one of the ordinary cells, or of a special lateral branch, as in 



2 78 



PLANT LIFE. 



the filamentous algae and fungi (figs. 307, 308). In the 
thallus of multicellular algas it may be the terminal cell of a 



a A 




Fig. 308. — Sex organs of water flannel {I'aucheria sessilis). A, a portion of filament 
with two lateral branches, a, Ag. In a the spermary has already heen divided from 
the body cavity by a partition wall. In r'x , a partition will form at juncture with main 
axis (see fig. /■). when . , becomes the ovary. B, the ovary, mature, having opened 
and extruded .v/, a portion of the protoplasm.. What remains is the egg. The chloro- 
plasts have accumulated, leaving a clear receptive spot opposite entrance of ovary. ( , 
sperms, which escape at maturity from A, <i. D, ovary with egg about to be fertil- 
ized; the sperms have collected at the opening. A, />', /», magnified about ioodiam. 
C, magnified much more (about 350 diam.?). A, />, after Sachs; />', C, after Prings- 
heim. 

branch or, in the leaf-like forms, a cluster of surface cells. 
In Fucus the spermaries (figs. 309, 310) are terminal cells 
of much-branched hairs which J 

develop from the surface cells 
of a narrow-mouthed pit like 








Fig. 309.— A portion of a branched hair from a conceptacle of bladder wrack (/■:,, us 
vesicutosus). The darker cells are the spermaries. Magnified 160 diam. — After 
Thuret. 

Fig. 310. — Spermaries of Fucus vesiculosus, showing the escape of the sperms. Magni- 
fied 350 diam. — After Thuret. 



SEX UA L RE PROD UCTIOX, 



279 



that for the ovaries (fig, 326). (See also fig. 42.) The 
sperms are set free by the rupture of the wall of the spermary. 
382. A compound spermary consists of one or more cells 
in which the sperms are to be produced (each correspond in- 
to a simple spermary), surrounded by a wall formed of a 
single layer of cells (rarely more). Compound spermaries 
are found only in Characese, mossworts, and higher plants. 
The spermary is a spherical or elongated sac, raised upon a 
stalk, or sessile ; free upon the surface of the plant, or sunk 
in a pit (fig. 311). The cell in which each sperm is formed 




Fig. 



longitudinal section ot a male head of Marchantia. t, portion of 




thallus ; ha, enlarged head or receptacle; a, spermaries, sunk in pits opening at 0. 
Magnified about 15 diam. />', compound spermary. a/, its wall, surrounding the 
immense number oi minute regularly arranged sperm mother cells; st, its stalk. 
Magnified about & 1 diam. —After Sai hs. 



is called a "sperm mother cell." Each contains a single 
nucleus which enlarges to form the sperm of that cell (fig. 
312). The sperms arc set free by the breaking down of the 
walls of the mother cells at about the same time that the 
outer wall of the spermary is ruptured by the destruction of 
one or more of its cells. 

The form of the vegetative body of the gametophyte in all 



2 SO 



PLANT LIFE. 



but the seed plants was described in Part I. The forms of 
the spermaries are as follows: 

383. Chara. — The compound spermary of Chara (fig. 
313) consists of a spheri< al case composed of four triangular, 
plate-like cells; from the inner face of each projects a 
handle-like cell to whose end are attached 24 filaments, each 
composed of 100-200 disk-shaped cells. Each of these con- 




Fig. 312. — Development of a sperm of a liverwort I Pellia epiphylla\. n, mother cell 
with nucleus, the latter approaching the wall ; 6 to h, nucleus elongating and curving 
into an arc, and finally a spiral coil; e, an edge view, showing origin of cilia from 
peripheral protoplasm ; /, also an edge view; k, mature sperm, free. Magnified iooo 
diam. — After ( luignard. 

tains a sperm; so that each spermary produces 20,000- 
40,000 sperms. 

384. Mossworts and fernworts. — In the mossworts the 

spermary is a stalked body, whose internal cells are the sperm 
mother cells, the outer laver forming the spermary wall (fig. 

In the fernworts the spermary is sessile and the number of 
mother cells is much smaller (fig. 314), corresponding to the 
reduction in size of the gametophyte (see • 395)- When 
the gametophyte is greatly reduced, as in the club-mosseSj 
a single spermary only is formed, which is even larger 
than the rest of the gametophyte (fig. 315). 

385. Seed plants. — In the seed plants the male gameto- 
phyte begins to be formed before the microspore leaves the 
sporangium. In gymnosperms the spore divides into two to 
six cells, one or two of which represent the vegetative part 



SEXUAL REPRODUCTION. 



28l 




Chara. bear- 



ol" the gametophyte and the others the spermary (fig. 316). 
In angiosperms the vegetative part seems to have vanished 
and the two cells which are formed constitute the spermary, 
the smaller representing 
the sperm cells and the 
larger the wall cells (fig. 
317; compare fig. 315). 
Sometimes, indeed, the 
smaller cell is only repre- 
sented by a nucleus, no 
partition wall being pres- 
ent. Thus, the spermary 
in all seed plants has almost 
become a simple one again 
by reduction from the com- 
pound spermary of their 
ancestors 

reduction of the male game- 
tophyte, that is, to a sex 
organ alone, almost all trace 
of resemblance to a plant 
has been lost, and it is diffi- 
cult to think of the pollen- 
grain (microspore) as pro- 
ducing a real plant. This 
male plant, though ex- 
tremely small and simple 
even when mature, is the 
exact homologue of the 
larger male plant produced 
by the spores of the mosses, ferns, horsetails and selaginellas. 
386. Pollen tube. -The maturity of the male gametophyte 
is reached only alter the microspore has been caught by the 
moist surface | fluid in the micropvle or on the stigma | pro- 



By this extreme Fig. 313.— A, part of a "leaf 

ing sexual organs. /\ leaf; p. undeveloped 
"leaflets"; 0', leaflet; /3", leaflets of the 
branch, sc; the dark oval body is the ovary 
containing the fertilized egg; ,v, five cortical 
cells which have grown spirally around the 
ovary proper and become adherent to it ; 
they terminate in . , the five crown cells, be- 
tween which the sperm makes its way to the 
egg; ,1. the spermary, showing four of the 
s toothed plates of which its wall is composed, 
and the center ot each to which on the inside 
the handle cell is attached. Magnified 33 
diam. /•'. longitudinal section through young 
"node" of a "leaf " of ( lhara, showing origin 
and young stage ot sexual organs. / and in 
stand in the c omers ot the adjacent tnternodal 
.ells; between them is the thin nodal cell 

from which arise ;< and the sexual organs .vX- 
and ,1 ; br, cortical tells co 
is the young ovary not yet overgrown by the 
cortical cells at its side's. ,,. the spermary, 

shows four wall cells outside, from which 
their handle cells have just been divided; 
all too young to shew relative sizes or shapes. 
Magnified 2 1" diam Alter Sat hs. 



282 



PLANT LIFE. 



vided to receive it. The wall cell remains undivided and 
grows to form an unseptate filament, called the "pollen 
tube" (figs. 317, 318, 319, 321, 322, 323). In gymno- 





Fig. 314. 

Fig. 314. — Vertical median section of the mature spermary of a fern [Adiantutn 
capillvs-veneris). /. adjacent cells of gametophyte (figs. 74, 77) j , ( , spermary, show- 
ing wall composed of three cells, the two lower (above and below letter a) being ring- 
like. The chloroplasts have accumulated on the inner face. The interior cell, origi- 
nally single, has divided into a number, the sperm mother cells, which at this stage are 
loosened and contain each a fully developed coiled sperm. Magnified 550 diam. — 
After Sachs. 

Fig. 315. — A vertical median section of the gametophyte of Selaginella stolonifera. 
/>, a single cell representing the vegetative part of the gametophyte (compare figs. 74, 
314) ; w, the cells forming the wall of tile spermary; ,f, the mother cells of the sperms, 
each containing one sperm and now loosened from each other. The gametophyte with 
its single spermary scarcely exceeds the size of the microspore which produces it and 
therefore only just bursts the outer wall of the spore. The solution of the wall cells 
w allows the sperms to escape. Magnified 640 diam. — After Strasburger. 

Fig. 316.— Diagram of the gametophyte of the larch (Larijc Europaa), formed in the 
microspore. /, the vegetative cell ; st , two stalk cells of the spermary; s, cell whose 
nucleus subsequently divides to form two sperms (the walls of the mother cells not 
forming) ; w, the wall of the spermary which remains undivided. Compare fig. 315. 

sperms this penetrates the megasporangium (ovule body) and 
reaches the female gametophyte on whose surface are formed 
the ovaries (figs. 319, 320, 321, 322). In the course of its 
development the sperm cell loosens itself and migrates down 
the tube. Its nucleus is set free by the disorganization of the 
wall of the cell (if formed) and usually undergoes division, 
thus making two or more sperms (figs. 321, 322). These 
escape through the ruptured wall of the end of the tube, 
pass between the neck cells of the ovary and so fertilize the 

egg (11 39 3> fi g- 32i)- 

In angiosperms, in order that the sperm may reach the 
egg, the pollen tube must grow through the tissues of the 
stigma and style, or pass down the style canal to the interior 



SEX UA L REP ROD UCTION. 



283 



of the ovulary, then through the micropyle (fig. 323), and 
finally penetrate the megasporangium. The sperm nucleus 
then fuses with the egg nucleus (see ^[ 369). 





Fig. 317- 



Fig. 31 



Fig. 319. 



Fig. 317. — Gametophyte of the pinesap (Monotrofla Hypopitys). <?, microspore show- 
ing two cells; the smaller being the sperm cell and the larger corresponding to the 
wall of the spermary, undivided. /■. the same, 6 hours later, showing the pollen tube 
developed from the larger cell. The smaller one has become disorganized ami its 
nucleus isttll undivided into sperms! and that of the larger cell have migrated into the 
tube. Magnified too diam. — After Strasburger. 

FlG. 318. — One stage in the fertilization of the egg of an orchid {Orchis latifolta). The 
pollen tube, /», has entered the narrow micropyle, «/, of an ovule, and reached the 
megaspore e, the upper half of which only is shown with three eggs (two imp rfi 1 1), 
In the pollen tube, just above and below the entrance of the micropyle, are the two 
sperms, s. s' . Magnified 3in.di.1m. After Strasburger. 

1 1 11. Longitudinal section through the ovule oi the larch and the placental scale 
to which it is attached. /, placental stale; ^, vascular bundles; ;/. megasporangium ; 
i, integument; . , female gametophyte inside megaspore wln.se limit is shown b) oval 
line; ,;, ovary;/, pollen-tube. Magnified 14 diam. — After Strasburger, 



The growth of the spermary as a tube within which the 
sperms may migrate to the egg is necessary because the female 
gametophyte is forced to develop within the megaspore, 
which is not released from the sporangium. In angiosperms 
the further enclosure of the megasporangia in the sporophyll 
(carpel) makes it necessary for the tube to be sufficiently long 



284 



PL A. XT LIFE. 



to traverse the pistil. Pollen tubes may, therefore, grow 
10-15 cm. in length. Usually the older part of the tube dies 




Fig. 322. 



Fir,. 320. — Anterior fourth of female gam'etophyte of spruce {Picea exceka), showing 
two ovaries. <\ tissue ot gametophyte (endosperm); a, egg; k. nucleus oi egg; /;, 
neck of ovary (the line does not reach the neck, which is situated in a depression of the 
plant below // : the shading shows the side (d this slope); kz, neck canal cell. See fig. 
321. Magnified 50 diam. -After Strasburger. 

Fig. 321.— A portion of the ovary of the spruce, seen as in fig j ■■ but magnified 165 

diam. The cell kz of lie,. 320 has bei mm .h -. u j.ini/ed to make way for the pollen 
tube,/, which has pushed between the neck cells and reached the egg, r, into which 
one of the sperms in its tip is about to enter, g, tissue of the female gametophyte.— 
After Strasburger. 
Fig. 322. Upper part of ovule of red cedar, with integument removed. >ni, mega- 
sporangium ; ctl, female gametophyte with three ovaries oi .11 luster of six ; /, pollen 
tube. Each ovary shows an elongated egg and above the small neck cells. The left- 
hand pollen tube has two sperms about to pass between neck cells into an egg. Magni- 
fied 67 diam.— After Strasburger. 



as the tip advances. The food needed is chiefly derived 
from the cells of the stigma and style which it disorganizes. 



SEXUAL REPRODUCTION. 



285 



387. The egg. — The egg is larger than the sperm, usually 
non-motile and fixed. In aquatic algre the egg is sometimes 




Fig. 323. — Diagram of a lun^iti.iuni.il >cl tii.n of a pistil with one ovule, s, stigma, on 
which are lodged two pollen grains ; ; . style ; a, 01 ulary ; /. >/, at, //, together form 

the Ovule ; /, stalk ; //, niega>poi,mgium ; ,; /', outer integument ; //. inner integument ; 
r. megaspure. will) nucleus which is to develop later into vegetative part ol female 
plant; i, antipodal cells ; k, egg, and near by another ; m, micropyle j /, polli 

entering it and reaching egg. -Alter I.ucrssen. 

free, escaping from the ovary in which it is produced, and 
being fertilized by the sperms, which arc likewise tree in the 
water, as in Fucus (fig. 324). Sometimes the egg itself is 
ciliatedand hence motile. In these cases it meets the motile 
sperms in the water. 

The form of the egg is much less variable than that of the 



(86 



PLANT LIFE. 



sperm. It is almost always ovoid or globular. The small 
amount of body protoplasm of the sperm may be looked upon 
as merely accessory. That of the egg, however, is usually 
abundant and well supplied with reserve food, and it takes 
part after fertilization in the formation of the new plant. 

388. The ovary. — The organ in which theegg is produced 
is the ovary (oogonium, carpogonium, or archegonium). 
Usually but one egg is produced in each ovary, though as 
many as eight are formed in the Fucacere 
(fig. 327). The ovary is either simple 
or compound. 

389. A simple ovary consists of a 
single cell, the bulk of whose proto- 
plasm becomes one egg (or several).. ($ 





324. Fig. 325. 

Fig. 324. — Egg of Fiichs as it floats in sea-water, surrounded by many sperms, one of 
which eventually plunges into it, unites with its nucleus and so fertilizes it. Magnified 
350 diam. — After Thuret. 

Fi<;. 325. — Portion of two ovaries of an alga {Spkeerofilea annulina). The upper part 
contains two eggs, and a number of sperms which have entered through the pore at 
the side. The lower egg of the two shows the receptive spot above. A sperm is 
partially imbedded in the protoplasm of this part in process of fertilization The 
egg in the lower ovary has been fertilized and has secreted a thick wall, thus becom- 
ing a resting spore. Magnified 500 diam. — After Colin. 



A portion of the protoplasm of the ovary is almost invariably 
excluded from the egg (B, fig. 308). The sperms reach the 
egg either through an opening formed in the wall of the 
ovary (D, fig. 308, 325), or through a tube formed by the 
spermary, which penetrates the ovary (fig. 307). 



SEX UA L REPR OD U CTION. 



287 



Simple ovaries occur only in the algseand fungi, where they 
are known as oogonia or carpogonia. They are either pro- 
duced by the modification of one of the cells of a filament 
(fig. 325), or they are the terminal cell of a special branch 
(fig. 308). Usually the ovary is decidedly larger than the or- 
dinary vegetative cells. The fertilized egg often becomes a 
resting spore (fig. 325). 

in the higher algae, especially the marine algae, the ovaries 
are often aggregated in special pits, the conceptacles, as in 




m 



Fig. 326.- A section through a female conceptacle of bladder wrack (Fucks vesiculo- 
sits); showing form <il pit. the numerous hairs with which it is lined, and ovaries in 
various stages . . t development. In the tissue about the pit note the cortex oi densely 
plated cells and the loose network of filaments in the interior. Magnified 50 diam. — 
After Thuret. 

Fucus (figs. 42, 326). Here the ovary is formed by the en- 
largement of the terminal cell of a two-celled outgrowth from 
the surface (\'\y;. 327). The eight eggs are set free and are 
fertilized in the water 1>\ the motile sperms (fig. 324). They 
grow at once into new plants. 

The simple ovary is surrounded in Chara (fig. 313) by a 
jacket of spirally coiled cells, which grow up from beneath it 
and make it look as though it were compound (•' 390). 



288 



PLANT LIFE. 



The most highly developed simple ovary (the carpogonium) 
occurs in the red algae, in which it is often differentiated into 
the ovary proper (which does not always form a distinct egg | 
and a long branch, the receptive apparatus, or trichogyne, 
to which the sperm adheres and through which its nucleus 





Fig 329. 

Fig. 327. Ovary of bladder wrack (Funis vesicuiosus), with some of the hairs. The 
ovary is raised on a stalk cell ; it contains 8 eggs, of which 6 are shown. Magnified 
160 diam. After Thuret. 

Fig. 328.— The ovary of a red alga {Nemalion multifidum). A , in process of ferti- 
lization, rco, egg nucleus (a dark chromoplast lying near); sp, sperm which has ad- 
hered to the trichogyne t and caused the absorption of the wall there : ns, the sperm 
nucleus on the way down the iii. Imumh- /•'. ,1 later stage, no and ns about to unite. 
Magnified about 600 diam. — After Wille. 

I'ii. \ In. null nt .1 red sf.iweed ( rolyslfihoniti ofiaca) bearing cystocarps (the 

black dots). See fig. 330. Natural size. — After ECUtzing. 



travels to the ovary proper (fig. 328). The result of fertiliza- 
tion is the production, often by a very complicated process 
of growth, of a spore-producing body, the cystocarp (figs. 
329, 330). The cystocarp is, in part, the homologue of the 
sporophyte phase of higher plants. From its interior non- 



SEX UA L RE PR OD UCTION. 



289 



sexual spores arise (fig. 330), which produce the gametophyte 
again. 

390. A compound ovary consists of a central row of cells 
(each of which is homologous with a simple ovary) surrounded 




Fig. 330. — A , a bit of a red seaweed bearing a mature cystocarp ; seen from the side. 
The spores show through the translucent wall. />'. a diagram of a section through the 
same, showing spores as enlarged terminal cells of twigs arising from a basal cell of the 
cystocarp. The shaded parts arise from the fertilized egg (= a sporophyte), the case 
developing by induced growth. Magnified 25 diam. — After Falkenberg. 

by a wall composed of one or more layers of cells. Of the 
central cells only the lowest produces an egg. The upper 
ones break down into mucilage, by the swelling of which the 
ovary is opened, and by its escape in whole or part a canal is 
formed leading to the egg (fig. 332). Down this canal the 
sperms make their way, and one fertilizes the egg. 

The compound ovary is known as an archegonium. When 
best developed, it is a flask-shaped structure [f\i;. 331) con- 
sisting of a body and a neck. In the body is the cell con- 
taining the egg. Compound ovaries may be stalked, sessile, 
or sunk in the tissues of the gametophyte. They are found 
only in mossworts, fernworts, ami seed plants. In the latter. 
however, they are simplified out of all likeness to the form 
dese lilted. 

391. Mossworts. — When the gametophyte is differentiated 
into stem and [eaves, as in mossworts alone, they are formed 
upon the stem. Usually several are developed in the same 
neighborhood, when they are generally protected by over- 



290 



PLANT LIFE. 



arching leaves (fig. 331). In the same cluster there may be 
spermaries, or these may be on a different part of the same 
plant, or on another plant. 





Fig 33" 



Fig. 332. 



Fig. 331.— Longitudinal section through the tip of a shoot of a moss (Funaria hygro- 
metrica). st, stem ; />, leaves protecting the ovaries a. Magnified ioo diam.— After 
Sachs. 

Fig. 332. — A vertical section of the gametophyte of a fern ( Pteris serrulata). g, vege- 
tative tissue of gametophyte, with chloroplasts ; e, .body of ovary sunk in gameto- 
phyte. surrounding the spherical egg; «, neck projecting and curved; /«. mucilage 
formed by disorganization of canal cells and escaping, having pushed apart terminal 
cells of neck. Magnified 260 diam. — After Strasburger. 

392. Fernworts and seed plants. — When the gametophyte 
is a thallus, as in fernworts and seed plants, the ovaries are 
borne on the surface of the thallus, partially or wholly sunk 
in its tissue. In the ferns, they arise upon the under surface, 
near the anterior end (fig. 74), and have the neck only pro- 
jecting (fig. 332). In the horsetails the ovary is still more 
deeply sunk. In the selaginellas the gametophytes are male 
and female, the male arising from the microspores (fig. 315) 
and the female from the megaspores (fig. 333). Both are 
small, scarcely larger than the spores in which they grow. 
The ovary is completely sunk in the female gametophyte and 



SEXUAL REPRODUCTION. 



2 9 I 



is much simplified, the neck-cells and the egg being the only 
distinct parts of maturity. 

393. Gymnosperms. — In the gymnosperms the female 
gametophyte is not large enough to burst the megaspore which 




spin 



Fig. 333. — Longitudinal section of the female gametophyte of Selaginella Martensii. 
//, d, (/, the body of gametophyte; »-, r, rhizoids (rudimentary) on its surface; a, an 
Ovary whose egg failed of fertilization; e, embryo developed from fertilized egg; its 
Cell-structure is not shown, but the various members are begun ; .r, suspensor ; st, stem; 
/, /, primary leaves ; rt, root; /, foot ; e ', a younger embryo, with cell-structure shown, 
the letter standing in large suspensor cell ; spnt, wall of megaspore. Magnified 12c 
diam.- After Ffeffer. 



remains enclosed in the sporangium. Upon its surface are 
formed several ovaries, each reduced to an egg and two to four 
tiers of neck-cells (figs. 320, 321). 

394. Angiosperms. — In the angiosperms the female gam- 
etophyte is so simplified that it is represented only by a few 
cells, among which may be recognized at least one egg (e, 
fig. 334), and possibly two others, s, s. The ovary has been 
reduced to nothing but an egg, and the full development of 
the gametophyte seems to be delayed until after the egg is 



2 9 2 



PLANT LIFE. 



fertilized. In these plants, therefore, we return to a con- 
dition which is scarcely an alternation of sexual and spore- 
producing phases, because the 
sexual phase is nearly obliterated 
by reduction. 

395. Relative size of gameto- 
phyte and sporophyte. — The ac- 
companying diagram (fig. 335) may 
roughly illustrate the history of 





Fig. 334. 



Fig. 335- 



Fig. 334.— End oi megaspore ol I\<Iy^ouii /// liivaricatum. e, egg; s, s, synergi- 
dx, probably sterile eggs. Below e the nucleus from whose divisions arise the cells 
"I the belated gametophyte Magnified 540 diam Alter Strasburger. 

Fio J35 Diagram representing the reduction of gametophyte and increase in sporo- 
phyte from lower to higher plants, a, green alga- ; /-, red alga-: r. liverworts; </, 
mosses; e, ferns ; y, club-mosses; .i,-, gymnosperms ; /;. angiosperms. Original. 

development of these phases in the vegetable kingdom. 

The gametophyte phase is represented by the dotted area. 
It has its greatest development in the lower algse and fungi, 
where it constitutes the whole, diminishes at first slowly and 
then rapidly. After the fernworts are passed it constitutes a 
relatively inconsiderable part of the plant and almost disap- 
pears among angiosperms. Of the sporophyte, represented 
by the white area, the reverse is true. The lines (tossing 
the diagram at various levels show by their length in the 
white and black areas the relative importance of the two 
phases in the groups indicated. 



SEXUA L REPROD UCT10N. 



293 



Loss of sexuality. 



396. Among fungi. — Though descended from ancestors 
possessing sexual organs, certain groups of plants have lost this 
mode Ox" reproduction and rely wholly upon non-sexual 
methods. Such are the higher 
fungi. The lower forms only 
have sexual organs. These fungi 
show their- relation to algae by 
retaining in part or wholly aqua- 
tic habits. In Cysiopus, for ex- 
ample, at a certain stage zo- 
ospores are produced ; and these 
are generally characteristic of 
aquatic plants, though Cystopus 
has become a parasite upon land 
plants. Many aquatic fungi are 
known, most of which grow 
upon dead plants or animals 
(espe< ially insects) which have 
fallen into the water. Not only 
do many of these lower forms 
produce zoospores, but the form 
of their sex-organs and mode 
of union remind one immedi- 
ately of similar structure and 
action in common algae. Com- 
pare, for example, the sex- organs 
in Vaucheria (fig. 308) and those oi Achlya (fig. 336). 

Some fungi possess sex-organs which are functionless, 
although the egg de\ elops as though it had been fertilized I fig. 
336). But in most, all trace of sexual organs has disappeared, 
though many produi e spore-bearing structures, the fructifica- 




Fig. 336. — A. Functionless 
of a fungus (Achlya <■ 

with 'i eggs . 
spermaries from branches ol same 
liyplia form fertilizing tube which re- 
mains closed. /•'. eggs which have 
tini; spuii's w itliout ferti- 
lization. M.i.unilu-il .■!•-•. iliam. — After 
s.n hs. 



294 PLANT LIFE. 

tions ( c 314) which are homologous with those known to arise 
from the fertilized egg and adja< ent parts. In all these cases 
the fructification may be considered the homologue of the 
sporophyte of higher plants, for, even though its origin is 
now purely vegetative, this has come about by reduction from 
more perfect ancestors. 

397. Apogamy. — In certain of the higher plants sexual re- 
production is sometimes replaced by a process of budding, 
which differs from reproduction by brood buds ( c 361 ff . ) 
in giving rise to the other phase from that on \vhi< h the bud 
arises. Some ferns, for example, regularly produce upon the 
gametophyte a bud which grows into a sporophyte, the sex- 
organs being functionless. This process is called apogamy. 

398. Polyembryony. — Among the seed-plants a budding 
of the megasporangium, instead of the fertilization of the egg, 
ma}- produce an embryo. Except that the embryo so pro- 
duced suspends its growth and becomes a part of a seed, such 
reproduction is in no way different from that by brood buds 
(^[ 361 ff.) It is common in the orange, and often results in 
the formation of more than one embryo in the seed. 

Results of sexual union. 

The immediate result of the coalescence of a male and a 
female gamete is the formation of a cell capable of producing 
a new plant, i.e . a spore. The first step toward this is the 
formation of a wall about the spore. It may then grow at 
once into a new plant, or it may remain dormant for a longer 
or shorter time. 

399. Resting spores. — In the latter case it is called a 
"resting spore." To protect itself, it thickens its-wall, often 
very greatly. It may then escape from the parent by the 
breaking of the ovary in which it lies, but more commonly it 
remains enclosed until set free by the death of the parent 



SEXUAL REPRODUCTION. 295 

and the decay of the ovary. Such are the resting spores of 
Spirogyrciy Mucin-, Cystopus, and Chara.* 

400. Embryo. — In the other case the sexually produced 
spore develops at once. Except in the brown seaweeds, 
whose eggs are ejected into the water before fertilization, the 
spore remains enclosed in the ovary, within which it begins 
to form an embryo. 

401. Induced growth. — As a consequence of this develop- 
ment, growth is induced in the ovary itself and the parts 
adjacent. In the mildews the ovary produces one or more 
asci (fig. 224), while the hyphae near by branch profusely and 
cover the developing internal parts with a thick false tissue 
(figs. 223, 337), the whole constituting a fructification. In 




Fig. 337. — Formation of t he " fruit" in a mildew (Rrysiphe Cichoriacearum). a, 
threads of mycelium ; i, spermary ; r, ovary ; </. the ovary after fertilization, show- 
ing tin branches from hypha beneath ovary covering it; e, later stage, showing 
these branches coalescent and dividing by partitions to form a false tissue. (Com- 
pare fig. 223.) Highly magnified. — After < Ersted. 

red seaweeds the ovary and adjacent parts finally form the 
cystocarp (fig. 330). In mosses the ovary grows extensively 
(fig. 33$), but is finally torn loose and carried up on the 
embryo and becomes the loose hood, which is usually lost 
early. The stem also enlarges beneath the ovary and forms 
a sheath around the embryo (fig. 338), which grows down- 
ward into the parent though not organically connected with 

*It should be remembered that thick-walled "resting -ion-" arc also 
formed vegetatively. Sec ■ jo8 



ig6 



PLANT LIFE. 



it. At the same time the neighboring leaves are stimulated 
to increased growth. 

In fernworts the sexual plant is stimulated by the growth 

of the embryo within it, and enlarges considerably. 

But it is soon outgrown by the young sporophyte, 

to which it supplies nourishment until leaves are 

produced and it is able to feed itself (figs. 76, 77 

78). 

402. Seed.— In all but the seed plants the de- 
velopment of the embryo is uninterrupted until 
a mature sporophyte is 
formed. In seed-plants 
the embryo develops to a 
stage, and then 





Fig. 338. Development of the embryo sporophyte of a moss {Funaria hygro- 
metrica\ A, longitudinal section ol the ovary, <5, £, A, shortly after fertilization 
of egg which has developed into the embryo, ol which J is the apical growing point 
and /' the b isal, or foot ; /., /.. body of ovary ; //, tile base of the neck. /•', longi- 
tudinal section through apex of stem and leaves. Two Ovaries are seen ; one has 
failed of fertilization ; the other, c, has enlarged I" a< i ommodate the embryo, _/", de- 
veloping inside it ; //. its neck, now withered. ( ', longitudinal section of same, older; 
f, the embryo has grown downward into the apex ot sirni : tin- ovary, . . has still 

further enlarged and indeed outgrow n the embryo, forming a bladdery case around 

its base and elsewhere a close sheath for it ; /;, the neck. Around the embryo, where 
it enters the stem, the latter has grown up as a sheath to whose edge the base of 
ovarv is still attached. A little later the ovary will be torn off at this point and will 
!„• lifted on !h. elongating sporophyte as a dry membranous sheath, the calyptra. 
.1 , magnified 500 diam. ; />' and C' about 65 diam. — After Sachs. 



SEXUA L RETROD UCTION. 



297 



ceases to grow. With suitable protection and food-supply 

it is then cast off as a seed (see further «[ 408), and usu- 
ally after a dormant period continues its development until 
mature. 

403. In gymnosperms. — The growth of the embryo from 
the egg in the gymnosperms stimulates the whole gameto- 
phyte. This grows as rapidly as the embryo, which pushes 
its way into it and remains completely surrounded by it (fig. 
339). The whole ovule is also stimulated to growth. The 
sporangium increases for a time, but is so crowded between 
the growing gametophyte within and the hardening integu- 
ment without that it is mostly absorbed (fig. 339). The in- 
tegument grows for a time 
to accommodate the struc- 
tures within, but its tissues 
finally become in whole or 
in part thick-walled, form- 
ing the seed- coat. In a few 
gymnosperms (Cycas) its 





h 

Ki<;. 339. Fig. 340. 

Fig. 33q. — Longitudinal section of the seed of silvrr fir i.//>/V.v /V, / 7 n.it, i\, showing 

straight embryo with several primary leaves in center of the endosperm (dotted); 

m, the micropyle, The integument lias become the testa (shaded with radial lines). 

Between the testa and endosperm are the remains of the sporangium. Magnified 

about 5 diani Alter Kerner. 
FlG. 340. — Longitudinal section <il seed ,.1 , nail's. //, hilum (scar of attach 

ment); w, micropyle ; t, outer fleshy layei ol integument; //and 1V1, two hard 

layers,,) same ; f, thin eap-like remnant of sporangium ; /, gametophyte enlarged 

forming the 1 ndosperm : ,». eggs which faili ,1 ol I, rtili/ation ; <-w, embryo produt ed 
by a fertilized egg. Two thirds natural size. After Luerssen, 

outer parts become fleshy, and the seed looks like a large 
cherry. In the yew a second fleshy integument (an aril) 
grows up around the hard seed (fig. 247). At maturity the 
seed of gymnosperms thus consists of the embryo within 
(fig. 340, em) surrounded by the gametophyte, />, whose cells 



298 



PLANT LIFE. 



become filled with reserve food, constituting then the so-called 
endosperm; around this is the remnant of the sporangium, 
when more than a mere membrane, likewise stored with food, 
and <alled the perisperm ; while over all is the hardened in- 
tegument or iesta, often of unlike layers, /, if, in. 

404. Fruit. — In the conifers the sporophylls hearing the 
ovules and the axis from which they arise also grow. As tin- 
ovule is becoming the seed each sporophyll enlarges, but 
especially the placental out- 
growth (set' • 334), and the 
whole number, together with 
the enlarged axis, form the 
cone (fig. 341, 358). Some- 
times (as in the junipers) the 
sporophylls become fleshy and 
adherent, forming a berry-like 
body. 




34'- 




.;(-•• 



Fig. 341.— A mature cone ol .1 pine (Pinus sylvestris), the upper quarter cut away. 
sq, s</\ the placenta] si ales ; g; seeds ; <•«/, embryo in a seed, lust below the pla- 
cental scale which bears the lower seed e, may be seen part of the carpellary scale 
in section. Magnified about 2 diam. From liessey. 

Fig 342. — A placental scale of pine {P. sylvestris) seen from above; showing two 
winged seeds in place. .1/, micropyle ; «'//. limit oi si ed ; the parts beyond are Rat 
wings, formed by the splitting off of a layer ol tissue from the surface of the scale. 
Magnified about ; diam. Vtoxa Bessey. 



SEXUAL REPRODUCTION. 299 

When firm at maturity the cone scales open on drying, and 
the seeds, each with a wing attached, split off from the scale 
(fig. 342) and are shaken out. 

405. In angiosperms the development of the embryo 
stimulates the belated female plant to complete its growth, 
and the megaspore (embryo-sac) is soon entirely filled by it. 
This late-forming gametophyte is called endosperm, as in the 
pines. 

406. Endosperm. — The growing endosperm and the 
embryo sporophyte, which it surrounds, crowd upon the 
sporangium. This may, therefore, partly or wholly dis- 
appear. If, when the full size of the endosperm is reached, 
the embryo continues to grow, it may crowd upon the endo- 
sperm until a part or all of it is absorbed. The embryo 
sooner or later passes into a resting stage and ceases to en- 
large. In this dormant condition it remains for a time whose 
duration is chiefly determined by external conditions. 

407. Food. — The tissue of the endosperm is utilized by 
the parent sporophyte as a storehouse of food for the use of 
the embryo sporophyte when it resumes growth. If the 
embryo displaces the endosperm, it absorbs the reserve food 
therein, consisting of starch, oil, or aleurone grains (^[ 236). 
In case any tissue belonging to the sporangium remains, this 
also is utilized for storage. To distinguish it from the endo- 
sperm it is called perisperm. It is only occasionally present 
in any amount in this group of plants. 

408. The integuments of the ovule at the same time en- 
large, and finally become differentiated in such fashion as to 
((institute the seed-coats. The ripened seed, therefore, con- 
sists of the following parts: ( 1 ) in the interior, occupying 
various positions and of exceedingly variable relative size, the 
embryo; (2) immediate) \ around this, the endosperm or peri- 
sperm, or both; but either or both may be so shrunken 
and emptied as to be recognizable only by microscopic ex- 



300 



PLANT LIFE. 



ami nation ; (3) upon the exterior, one or two integuments 
more or less readily distinguishable from each other (figs. 
343> 344, 345)- 






Fig. 743.— Longitudinal section of fruit of black pepper, containing a single seed. /V, 
pericarp, showing two layers (the outer unshaded, the inner shaded by radial lines); 
sc, seed-coats ; em, embryo, surrounded by en, the endosperm ; /, perisperm. Mag- 
nified about 5 diam. — After Baillon. 

Fig. 344.— Seed of pansy, entire and halved, the latter showing the straight embryo, 
the endosperm (white and dotted), the seed-coats ; m, micropyle. Magnified about 
10 diam. — After Baillon. 

409. Fruit. — The growth of the embryo 
excites not only the tissues of the ovule to 
further development, but also the sporophylls 
(carpels) bearing the ovules, and not infre- 
quently even more remote parts. The carpels 
(PAytoiaVta an< ^ tne * r contents and adherent parts, when 
halved* ^show' fully developed, constitute the fruit. The car- 

b°rfo U nelt the P e,s are tnen knOWD as the pericarp. The 
and" neai-'b/sur 5 changes \vlii< h the parts undergo are chiefly 
"ndosperm! of two sorts — an increase in size and an altera- 
dtam! — ''After ti 011 °f texture. The increase in size requires 
no special explanation. The carpels may be- 
come dry at maturity, or may thicken and become soft and 
fleshy, or even juicy. In accordance with these differences, 
two sorts of fruits are recognized, namely, dry fruits and 
fleshy fruits. Between these, however, there is no sharp line 
of demarcation. 

410. Dry fruits. — If the pistil contain only one or two 



SEXUAL REPRODUCTION. 



30I 



seeds, it very often does not open at maturity. Consequently, 
the seed-coats ordinarily remain thin, and the protective 
function is put upon the pericarp. In some cases the carpel 
becomes adherent at an early stage to the surface of the 
ovule, and at maturity the pericarp is so firmly attached that 
it can scarcely be distinguished from the seed-coats them- 
selves. Such a change takes place in the fruit of most grasses, 
and the grain so formed is ordinarily mistaken for a seed 
(fig. 346). When dry fruits are one-seeded and indehiscent 



12 34 




Fig. 346.— A small portion from the margin of a transverse section of grain of oats, 
1, 2, pericarp; 3, seed-coats; 4, remains of the sporangium : 5-7, endosperm ; 5. 
gluten cells; 6, cells containing large compound starch-grains (compare fig. 174) at 
7 richer in gluten, with less starch. Magnified about 325 diam.— After Harz. 



the pericarp usually bears whatever special contrivances are 
necessary for the distribution of the seeds. (See further ^[ 
489 {{.^ If, however, the pericarp contains many seeds, it 
generally breaks at maturity to allow the loosened seeds to 
escape. The extent and position of the opening into the 
seed chamber or chambers are extremely various. In some 
cases the openings are so small as to be mere slits or pores 
(fig. 347). In others a more or less circular line of breakage 
forms a little door or valve which opens and closes with 



302 



PLANT LIFE. 



changes of moisture (fig. 348). In other cases the pericarp 
splits lengthwise into two or more pieces (fig. 340), or, less 





Fig. 347. 



Fig. 348. 



Fig. 347. — Ripe capsules of a wintergreen (Pyrola c/itoran//ta), showing dehiscence 
by pores. The opening is a short split at the middle of the base of each carpel. 

Natural size— After Kerner. 
Fie;. 348. — Ripe capsules of a bellflower (Campanula ra/>u>uuloides), showing 
small reflexed valves. Natural size. — After Kerner. 




Fig. 34g.—/f, capsule of violet split open at maturity, the seeds still attached to the 
parietal placenta;. />', three pods of Lotus corniculatus ; a, just beginning to 
1 r,<. k ; 6, split throughout, with the pie< es somewhat twisted ; < , empty ol seeds, the 
two pieces fully dried and twisted. Natural size.— After Baillon. 



SEXUAL REPRODUCTION 



303 



often, cracks transversely so as to loosen a lid (fig. 350). In 
the former case, if it is composed of two or more carpels, 
(1) the carpels may separate from each other along their 
original line of coalescence. If these carpels so separated 
contain only one or two seeds, they may remain indehiscent 
and behave like the simple pistils previously described ; but 





Fig. 350. 

Fig. 350 — Ripe capsule of pimpernell {Anagallis arvensis), opening by a lid. 

Magnified several diam. — After Baillon. 
Fig. 351. — Diagrams showing three modes in which capsules break as seen in trans- 

vt-rse sections. A, septicidal dehiscence; B, loculicidal dehiscence ; C, septifragal 

dehiscence. Modified from Prantl. 

if they contain several to many seeds, they also break along 
their inner edges (A, fig. 351). Or, (2) the carpels may 
split along the middle, ami also at the center of the ovulai v 
if it is more than one-chambered (B, fig. 351 ; A, fig. 349). 
Or, (3) the outer parts of the carpel may split away from the 
placentae, thus exposing the seeds (C, fig. 351). 

411. Fleshy fruits. — The changes which produce fleshy 
fruits consist in the transformation of certain parts of the 
pericarp into masses of thin- walled juicy cells. Other parts 
may remain unchanged, or may even become hardened. The 
inner part ot the pericarp sometimes becomes of a stony 
hardness, while the outer portion becomessoft and juicy. Such 



304 



PLANT LIFE. 



changes produce a fruit like that of the peach or the cherry. 
The pericarp encloses a single seed 
with delicate brown seed coats whose 
protective function has been com- 
pletely usurped by the stone (fig. 
352). In other cases, while the 
inner face becomes stony, the outer 
becomes fibrous, tough, and dry, as 
in the almond, walnut, and hickory 
nut. The outer part in the last even 




Fig. 352.— Fruit of the cherry, breaks regularly into four pieces 

halved, e, epidermis of peri- _,_.... . . _ 

carp; m, fleshy layer of Such frUltS flimisll a transition frOU 
pericarp ; en, stony layer of 



pencarp; .?, seed; cot, one the most perfect fleshy fruits to the 

of the pair of thickened seed- . . 

leaves of embryo. Natural dry fruits. In other cases the placentas 

size. — After Focke. . , 

become very much enlarged, and the 
whole of the pericarp becomes fleshy, as in the tomato. In 
others the outer part of the pericarp is hard and firm, while 
the inner becomes pulpy, as in the pumpkin and squash. 

412. Accessory fruits. — Parts adjacent to the carpels, 
either flower leaves or axis or both, stimulated to growth, 
frequently enter into the formation of 
fleshy fruits. These may be accompanied 
by either a fleshy or a dry pericarp. In 
the wintergreen berry the calyx grows 
thick and fleshy and surrounds a dry peri- 
carp, which cracks at maturity (fig. 353). 
In the strawberry (fig. 287) the torus be- 
comes greatly enlarged and fleshy, while 
the minute, one-seeded, dry fruits are 
scattered over its surface, imitating small 
seeds. The fig has the same parts, with 
the torus concave, instead of convex (fig. 
289). The apple consists of a fleshy torus carrying at its 
free end the withered calyx and enclosing the tough, thin 




Fig. 353. — Fruit of 
wintergreen (Ga ul- 
theria procum- 

fie/is), halved, show- 
ing thin (dry) peri- 
carp, surrounded by 
thickened fleshy 
caly x. Magnified 
about 2 diam. — After 
Gray. 



SEXUAL REPRl >/' < 'CTK >JV 



305 



pericarp | fig. 354). In the blackberry the receptacle be- 
comes fleshy, and each pistil forms a minute fruit like a 




Fig. 354. — Fruit of the apple. A, halved longitudinally; 
pericarp, enclosing seeds ; g, vascular bundles of the tit 
calyx leaves. One hall natural size.— After Focke. 



alved transversely. /, 
torus entering k, the 



cherry, adherent to its neighbors and to the pulpy torus. The 
raspberry is like it, except that the adherent mass of fruits 
separates as a cap from a firm torus (fig. 355). 

413. Multiple fruits. — If the flowers form a crowded in- 
florescence, either dry or fleshy fruits may be closely crowded 
at maturity. Under these conditions fleshy fruits frequently 
become adherent, and may thus constitute a multiple fruit 
quite similar in form to the fruit formed by the aggregated 





Fig. 355 



Fig. 356. 



Fir.. 3H5. — Vertical section of a flower of raspberry (Rubus idtrus), showing numerous 
pistils which form the caplike fruit over the enlarged torus; olla, and 



calvx all united .it base. Magnified about 2 <li. 
Fig. 156.— A, pistillate flower cluster ol white 1 

Natural si/e Alt. i P.aillon. 



Alter kerne 
ilberry; B, multiple fruit from same 



306 PLANT LIFE. 

carpels of a single flower. Compare the multiple fruit of the 
mulberry (each section from a separate flower whose floral 
leaves and pistil both become pulp}-; fig. 356) with such an 
aggregate fruit as the blackberry, in which each section is 
one pistil out of the many belonging to a separate flower (fig. 
355). The pineapple is similar to the mulberry in origin. 

Even more remote parts are stimulated to development by 
fertilization of the egg. The stem bearing the flower gen- 
erally grows and becomes stronger, to carry the fruit, espe- 
cially if large. The minute bractlets sometimes become 
highly developed beneath the fruit. The cup of the acorn 
and the husk of the hazelnut originate in this way as the 
nuts form. The similar husk of the beechnut and chestnut 
encloses more than one fruit. 

414. Distributive arrangements. — Since the seed plants 
abandoned the distribution of the megaspores and form both 
the gametophyte and the new sporophyte within the tissues 
of the old, it became necessary to adopt some other method 
whereby the young can be so scattered as to prevent them 
from coming into sharp competition with the parents. This 
distribution occurs at the time of maturity of the seed, i.e., 
when the embryo has become dormant, and the food store 
and protective coverings have been completed. The devices 
by which seeds are scattered are dependent upon the number 
and character of the seeds and the nature of the pericarp. 
Thus, one-seeded, indehiscent fruits must be scattered by the 
structures arising upon the surface of the pericarp or its ad- 
herent parts. On the contrary, seeds which escape from the 
pericarp have the distributive structures developed by the 
seed coats themselves. For distribution plants adapt them- 
selves so as to employ the agency of the wind, water, and 
animals, or they develop special mechanisms for casting off 
the seed as a projectile. A consideration of these adapta- 
tions belongs to ecology. (See Chap. XXVI.) 



PART IV: ECOLOGY. 

415. Definition. — Physiology, in its broadest sense, may 
be divided into physiology proper and ecology. Ecology 
is that portion of botanical science which treats of the rela- 
tions of the plant to the forces and beings of the world about 
it, as distinguished from physiology proper, which treats 
of the relation of the plant as a whole to the chemical and 
physical forces within it. The forces without the plant 
necessarily limit and modify the action of the forces within 
it; consequently it is quite impossible to draw a sharp dis- 
tinction between those subjects which belong to ecology and 
those which belong to physiology proper. Parts II and IV, 
therefore, will be found to overlap in many places. Several 
of the subjects already treated under physiology belong in 
part to the present section. for example, the movements 
of plants are due not to internal causes alone, but to internal 
causes as modified by external conditions. In this part only 
a bare outline of the adaptations of plants in form and habit 
to their physical surroundings and to other living beings i an 
be given. 

307 



I. NUTRITIVE ADAPTATIONS, 

| I. ADAPTATIONS OF FORM AND STRUCTURE 
TO ENVIRONMENT. 

CHAPTER XIX. 

FORMS OF VEGETATION. 

416. Adaptation. — The various physical conditions which 
make up the "climate" of any particular region of the 
earth's surface, together with the nature of the substratum 
upon or in which the plant grows, largely control the form 
and functions of the plants found in that region. Stated in 
other words, plants, in order to exist at all, are compelled to 
adapt themselves to the places in which they grow. This 
compulsion is on pain of death. 

417. The struggle for existence. — The competition be- 
tween plants is intense. Only a very small portion of the 
seedlings which start in any particular area can come to 
maturity. Far the greater number will be killed by being 
robbed of light and of water by the overshadowing leaves 
and interlacing roots of their companions. Since such com- 
petition exists, it is evident that only those best suited to the 
conditions under which they 'grow will have any chance 
whatever to survive. 

Not only are individuals subject to this competition, but 
all individuals of a particular kind (a species) may be de- 
stroyed in any region through the competition of other 
species better suited to the conditions of that region. 



FORMS OF VEGETATION. 309 

Through this competition between species one kind may be 
forced to migrate to some different region in order to main- 
tain itself. The capacity of a plant to adapt itself to a differ- 
ent environment determines the possibility of its occupying 
a new region, for here it must come into competition with 
other sorts, and can only maintain itself if it is capable of so 
modifying its form and structure as to adapt them to the new 
conditions, and that as well as or better than the occupants 
it finds in possession. In the beginning it was probably by 
competition between species that water plants were gradually 
adapted to an amphibious life, and then to a terrestrial life, 
all the while advancing in complexity; later some green 
plants adapted themselves to a parasitic or saprophytic life ; 
plants of moist regions gradually moved out and occupied 
even the deserts ; plants loving the shade adapted themselves 
to the direct light of the sun ; and so on, until all parts of 
the earth's surface and even considerable depths of the ocean 
have been occupied. 

418. Environment.— In order to understand the variety 
of factors which are acting upon any particular plant, it will 
be instructive to consider the conditions which surround the 
ordinary land plant. A portion of such a plant is imbedded 
in the soil, and the remainder rises into the air. The sub- 
terranean part is profoundly influenced by the size and form 
of the soil particles, as well as by their chemical composition. 
It is exposed to contact with water varying in amount, some- 
times from day to day and always from time to time during 
the year, holding many substances in solution in varying 
amounts and kinds at different periods. It is subject, also, 
to variations of temperature from day to day and from season 
to season. 

The aerial part of such a plant is exposed to greater or 
less variations of temperature from hour to hour, from day 
to night, from day to day, and from season to season. It is 



3IO PLANT LIFE. 

exposed to light varying in intensity from day to night and 
from day to day, and to light differing in direction from hour 
to hour of each day. It is enveloped by fogs or mists, or is 
pelted by rain, hail, sleet, or snow, and sometimes com- 
pletely buried in ice or snow. 

A plant has little or no power to alter any of the agents 
which act upon it, but it must be able to withstand the in- 
jurious ones, or even to turn them to its advantage. It 
would be difficult to conceive a more complex set of factors 
to which adjustment must be effected ; and the more since 
these conditions are combined with each other in an infinite 
variety of ways. Because the physical conditions vary in 
different parts of the earth's surface, the vegetation in each 
region differs from that in others. 

In any particular locality certain conditions of water, soil, 
air, temperature, light, and precipitation are likely to be as- 
sociated. It is possible, in a somewhat arbitrary way, to 
recognize four general sets of conditions to which plants must 
adapt themselves, in each of which the water supply is the 
predominant factor. It should be understood clearly, how- 
ever, that these sets of conditions pass into each other im- 
perceptibly. Corresponding to these four sets of external 
conditions, we may recognize certain characteristics in plant 
form and structure, which are likely to be as>ociated, and it 
thus becomes possible to distinguish four forms of vegetation 
corresponding to the four sets of external conditions. 

419. The first set of conditions consists of those charac- 
terized by no extremes. Both the air and the soil are moder- 
ately moist; the precipitation is distributed through the 
year, or at least through the growing season ; there is no ex- 
cess of salts in the water or in the soil ; the soil is usually 
enriched with organic matter, often in considerable amount. 
The plants which grow under these conditions are the ones 
most familiar to people in the fertile regions of temperate 



FORMS OF VEGETATION. 3 11 

climates. These may be reckoned as the average, or mean, 
plants, and are therefore called technically mesophytes. 

420. A second set of conditions is characterized by de- 
ficient water supply throughout the year, the amount of water 
present in the soil often being less than 10$. Such regions 
may be considered as regions of continuous drought. The 
plants adapted to these conditions are known as drought 
plants, or xerophytes. 

421. A third set of conditions, prevailing over compara- 
tively limited regions, is characterized by an excess of salts in 
Ike soil or water. These salts are chiefly sodium chloride 
(NaCl, common salt), gypsum (CaSOj, and magnesium 
chloride (MgCl). Plants which can live under these condi- 
tions are known as salt plants, or halophytes. 

422. A fourth set of conditions is characterized by an 
excess of water. The plants grow wholly or partly surrounded 
by water, or their roots are imbedded in a soil supersaturated 
with water, that is, containing at least 8o$. Such plants are 
called water plants, or hydrophytes. 

It will be noticed that the first three groups, namely, meso- 
phytes, xerophytes, and halophytes, are essentially land plants 
in distinction from the fourth group, which are water plants. 



CHAPTER XX. 

MESOPHYTES. 

423. I. Mesophytes show certain general relations to ex- 
ternal conditions, many of which are also shared by other 
forms. Except to these minor variations in the environment, 
they show no special adaptations ; or, rather, they are looked 
upon as the normal plants, and the ways in which others 
differ from them are spoken of as special adaptations. In 
reality, however, the general methods by which they adapt 
themselves to their environment, which are now to be con- 
sidered, are quite as much special adaptations as those shown 
by plants living in extreme climates. These adaptations will 
be discussed in relation to each of the main factors of the 
environment. 

424. i. Air. — The composition of the air varies little from 
place to place. It is only in those regions in which it is 
rendered impure by artificial means, such as the vicinity of 
cities and factories, and in the few isolated regions in which 
it is vitiated by natural means, as in volcanic regions, that 
any special adjustments may be looked for. Artificial vitia- 
tion of the air kills off certain plants. A few plants have 
adapted themselves to air in the neighborhood of fumaroles, 
where they are subjected to vapors containing large amounts 
of sulphurous acid. Whatever special adaptations are found 
are internal, since only the very simplest plants find it pos- 
sible to live in such conditions. 

The movements of die air, however, influence profoundly 

312 



MESOPHYTES. 313 

the form of plants. This they do indirectly by the shifting 
of sands in sandy regions, and by their effect upon the pre- 
cipitation and upon the moisture of the atmosphere. Winds 
increase evaporation from the soil and from the surface of 
plants, and thus directly influence form. Trees growing in 
wind-swept regions are always low, bushy-branched, with 
the trunk and limbs inclined to leeward. The twigs on the 
windward side are often dead. Forests in wind-swept regions 
often thin out to windward, the trees becoming smaller and 
smaller, finally being replaced by bushes which become 
sparser until no woody vegetation is present. The leaves 
upon such plants are small and often peculiarly spotted. 
These effects upon the form have been ascribed to the me- 
chanical action of the air, to the presence of salts when in the 
neighborhood of the ocean or salt lakes, and to the reduced 
temperature ; but probably none of these causes is to be 
looked upon as so efficient as the drying brought about by 
the prevalent wind. 

425. 2. Light. — Light affects plants directly through its 
influence upon their nutrition and upon the evaporation of 
water from their surfaces. In this way it affects (1) the rate 
of development. For example, the blossoming of flowers 
and the production of leaves occur earlier upon the sunward 
side of a tree or shrub than upon the other side. In the 
same cultivated crops of the north and south there will often 
be several days' difference in the total number between sow- 
ing and maturing. Thus barley at northern Norway, in 68° N. 
lat., matures in 89 days, while at Schonen, in 56 N. lat., it 
matures in 100 days. Since the total hours of illumination 
must be about equal, the longer days of the north enable the 
plants to produce more food, and so to mature more rapidly. 
The forcing of vegetables under glass by the aid of electric light 
during the night depends upon the same principle. (2) The 
form of plant parts is directly influenced by light. Plants accus- 




314 J PLANT LIFE. 

tomed to the direct sunlight and those accustomed to shad-' 
show profound differences in habit. Light plants are stocky and 
compact ; their stems are inclined to be woody, the leaves 
are usually folded or crisped aud often set at an acute angle 
with the direction of the light, and the surfaces are frequently 
hairy. In contrast, shade plants are slender and sprawling; 
their stems often thin and weak ; the leaves flat and smooth 
and set transverse to the direction of the light-rays, while the 
surface is slightly, if at all, hairy. (3 ) In inte rnal structure ; 
,- ajso, there are decided differences, particularly!!! the le a ves. 
(See %" 167, 438.) The leaves of light plants usually have a 
thick epidermis, often shiny, with lateral walls straight ; the 
stomata are frequently confined to the under side and often 
,sunk; the palisade cells are elongated, sometimes forming 

(two or three layers and occasionally appearing on both faces 
of the leaf. The shade plants, on the contrary, have a thin 
epidermis, often containing chlorophyll, with lateral walls 
often very wavy ; the stomata are produced on both sides of 
the leaves, and the palisade tissues are poorly developed. 
Light plants frequently have red cell-sap, especially in the 
epidermis of smooth plants, and their colors are always 
deeper, especially in the plants of high latitudes. Shade 
plants, on the other hand, are usually pale, rarely high- 
colored. 

426. 3. Temperature. — Temperature exercises an im- 
portant influence upon plants, both upon their aerial and sub- 
terranean parts. The temperature of the air is really much 
more important in controlling the adaptations, and con- 
sequently the geographic distribution, of plants than is light. 
The reason for this is to be found in the much more unequal 
distribution of temperature in various regions of the earth's 
surface. Moreover, temperature' affects every vital function 
of the plant, for each of which a maximum, minimum, and 
optimum point maybe determined. (See ^[ 186, 263.) The 



MESOPHYTES. 3^ 

variations in temperature to which plants are subjected require 
special adaptations. 

427. (a) Protection against changes of temperature. — 
These adaptations arc to be found in the presence of special 
cell-contents, such as oils or resins, which reduce the liability 
of those cells to freezing ; in the reduction of the amount of 
water in cells so that less damage results from freezing ; and, 
finally, in the presence of poor conductors of heat, such as 
scale-leaves and hairs in profusion, a jacket of old withered 
leaves, etc., all of which insure slow thawing if the plant is 
frozen. The winter buds of trees in temperate climates 
illustrate all of these adaptations. 

428. (l>) A dormant period is necessitated by low tem- 
perature during part of the year in temperate and arctic cli- 
mates. The period of vegetation in the higher latitudes is 
often very short. The same conditions prevail at high alti- 
tudes, with the same effects. In these regions, therefore, the 
plants are almost all perennials. In many cases the rudiments 
of flowers are formed in the year preceding that in which 
they are developed, in order that full opportunity may be 
given for the ripening of the seeds and fruits in the short 
growing season. Some plants adapt themselves to short 
periods of vegetation by the presence of evergreen leaves, 
which are ready at the first opportunity to resume their work 
of food manufacture. 

429. ( c ) The form of plants is modified by the tem- 
perature of the air and soil. Tow temperatures are also 
likely to bring about the formation of dwarf plants. 

430. (d The rate of development is strikingly influenced 
by variations in the temperature of the soil. The soil heat is 
derived from the sun and from the decomposition of organic 
matter within it. The sun is far the most important source. 
The amount of lnat absorbed varies with the exposure of the 
soil, its color, porosity, amount of water, and the duration of 



3I<3 PLANT LIFE. 

the sun's rays. The influence of the temperature of the soil 

is mainly indirect, acting through its effect on the water 
supply of the plant. 

431. (c) Moisture and precipitation. — The amount of 
moisture in the atmosphere largely determines the amount of 
evaporation from the surface of the plant. The relative 
amount of moisture in the atmosphere is exceedingly variable, 
and bears a direct relation to its temperature. Indeed, so 
closely related are the conditions of temperature, light, and 
moisture in the air, that the adaptations of shade plants, 
mentioned above, may be considered as the sum of the 
effects due to these three factors. It is difficult, if not im- 
possible at present, to say which are the effects of light and 
which of evaporation. 

Precipitation affects plants chiefly as it influences water 
supply. A few plants only of the higher forms are able to 
absorb moisture directly from the air, except as a last resort. 
(See % 196.) Many of the lower plants, such as the algae, 
lichens, and mosses, absorb rain instantly by their aerial 
parts. Some plants have adapted themselves to frequent and 
prolonged rainfall, bearing it often for months at a time ; 
other plants under such conditions lose their leaves very 
quickly. Rain-loving plants have their leaves furnished with 
elongated tips or with grooves and hairs to carry off the rain 
quickly. Their surfaces, also, are not readily wetted by water. 
Others protect themselves against the rain by adjusting the 
direction of their leaves to it so that a heavy, splashing rain 
strikes them at an acute angle. Others, by a movement of 
their leaves as soon as the sky is clouded, avoid injury from 
heavy rains. The branching of leaves in certain cases may 
be looked upon as a protection against heavy rainfall. 

The snow cover through cold periods is for many plants 
essential as a protection against low temperatures during the 
dormant period. Others have adapted themselves to growing 



MESOPHYTES. 3'7 

even in the midst of snow, putting forth their leaves and 
blossoms while still surrounded by melting snow. 

432. ( /') Soil. — Both the chemical composition and the 
physical properties of the soil affect plants. The latter arc, 
however, by far the most important. Here, again, the reason 
is to be found in the relation of the physical qualities of soil 
to the water supply. 

The water which permeates the soil takes up from it certain 
substances, and becomes thus a dilute solution of various 
salts. That the salts thus present in the soil water may affect 
the form of the plant is strikingly shown in the occurrence 
of certain species of a genus only upon soils containing lime, 
while others of the same genus are found only in soils free 
from lime. When the local distribution of corresponding 
species of the same genus within the same region is deter- 
mined by the presence or absence of lime in the soil, com- 
parison of them indicates the general effect of lime salts upon 
the plant. Plants growing upon lime are usually stronger 
and more densely hairy, often hoary, while those on other 
soils are smooth or furnished with glandular hairs. The 
lime-loving plants have bluish-green leaves, as contrasted 
with the grass-green. Their leaves are also more numerous 
and more deeply branched, the flowers larger and their colors 
dulkr and paler. 



CHAPTER XXI. 

XEROPHYTES AND HALOPHYTES. 

433. II. Xerophytes. — The plants of dry regions blend 
by imperceptible gradations with the mesophytes. They 
reach their best development in desert and rocky regions. 
Some, especially of the lower forms, grow in such situations 
that they must adapt themselves to become so dry at certain 
periods that they may be powdered. Such, for example, are 
a few algae, many lichens, mosses, and a few fernworts. 
Adaptations in these cases must be looked for in the character 
of the cell contents. 

Other plants must adapt themselves to endure dry periods, 
such as those occurring from day to day, or between the wet 
and dry seasons, by retaining in their bodies sufficient water 
to sustain life. The following are some of the chief methods 
by which plants adapt themselves to periodic or continuous 
drought. 

A. Adaptations for reducing transpiration. 



434. i. Periodic reduction of surface exposed. — -The 
dying away of an annual plant after forming its seed may be 
looked upon as an adaptation of this sort. Little evaporation 
occurs from the surface of the seed, which is thus adapted to 
withstand prolonged dryness. Perennial plants accomplish 
the same results when their annual shoots die off and leave 
only the rhizomes, tubers, and similar parts buried in the soil. 
Perennial plants with perennial shoots may drop their leaves 

318 




XEROPHYTES AND HALOPHYTES. 319 

during the dry period and form them again upon the return 
of the growing season. The fall of leaves in our woody vege- 
tation is a similar adaptation to the cold season. The rolling 
or curling of leaves is a common mode of avoiding evapora- 
tion. It is common in grasses ( fig. 357) and mosses. 

435. 2. The constant reduc- 
tion of exposed surface. — This 
B ^fl^ may be secured among the leaves 

by reducing them either in area 
f or in number or both, or by much 
ranching, with little green tissue 

A 
Fig. 357. — Transverse sections of a gra>-s leaf (Lasiagrostis). .1, open; A', rolled, 
when dry. The white plates are the ribs of mechanical tissue above and below a 
stele, one in each ridge ; the shaded areas are green tissue. The Stomata are located 
low on the sides of the narrow grooves between the ridges, so that when the leaf is 
rolled, evaporation through them is hindered. Magnified 16 diam. — After Kerner. 

Plants wi th bris t je-sh npr-' 1 "'■ "—d ie-shaped leav es (tigs. 10 1, 
358), those with permanently rolled leaves (fig. 359), or 
those with scale-like leaves I fig. 100 ) show thev arious phases 

of such adaptations^ KxtrenuT reduction oTsurface is secured 

by suppression of leaves. In this case any further adaptation 
depends upon the stems, which must also provide fornutritive 
work. The.se may take the form of leaves 1 see € 112); 
or the branches may be thick, rigid, and fleshy 1 fig. 360) ; 
or they may be thread-like or needle-shaped, as in the aspara- 
gus (fig. 105) ; or the stems themselves may reduce their area 
by becoming fleshy and cylindrical, prismatic, or spheroidal, 
as in the various forms of Cereus and melon <a<tuses (fig. 
1 10). 

436. 3. Movements of parts to reduce the illumina- 
tion. — Certain lea\es are adapted to a permanent profile 
position, that is, with the edges turned toward the sky. 



320 



PLANT LIFE. 



instead of the surfaces. (See ^| 285.) Others assume a 
profile position when the illu- 
mination becomes too intense. 
These positions, by placing the 
leaf surface oblique to the di- 
rection of the light rays, reduce 
the amount of evaporation very 
considerably. 

437. 4 Coverings, consist- 
ing of living or dead scale- 
leaves, stipules, leaf-bases or 
entire leaves, reduce transpira- 
tion by obstructing the free ex- 
change of air, or by holding 
water and so keeping moist the 
surfaces they cover. 

438. 5. Structural modifi- 
cations. — ■ These may occur 
either in the epidermis- or some 
internal tissues. (a) The epi- 
dermis may greatly reduce evap- 
oration by the formation of 
hairs in such profusion as to 
form a cover for the surface 
(figs. 361-364). Hairs in- 
tended to protect from evap- 
oration are usually dead and 

filled with air. Reflecting light from many points, they look 
white, and the surface seems hoary, or woolly, or silky. 
Hairs in the form of scales which overlap reduce the rate of 
evaporation by covering the stomata (fig. 365). -Iuirther__ 
adaptations~ot the epidermis are to be found in the pres- 
ence of a thick cuticle (fig. 367); the water-proofing of 
the whole of4he outer wall of the epidermis; the develop- 




. — Shoot of larch, with ripe 
showing needle-shaped leaves 
on dwarf branches ; scale leaves on 
main axis ; carpellary scales just peep- 
ing from between placental scales of 
cone. Natural size. — After Ke 



XEROPHYTES AND HA l.OPH YTES. 



321 



ment of two or more layers of epidermal cells (fig. 370) ; or 
the excretion of wax or of varii+*ff upon the surface of the epi- 



FTOXrs: 








Fig. 359. — Transverse section of a leaf of a heath {Tylanthus ericoides), showing 
revolute form. The stomata are on the under (concave) surface among the hairs, 
winch still further impede the transpiration. Magnified 130 diam. — After Kerner. 



dermis. The latter often becomes very thick, giving to the 
leaves a shiny appearance. Wax is usually in the form of a 




Fig. 36 



Fig. 360. — Prickly pear ( >puntia vulgaris) with Battened jointed stem and no 

leaves. About one fourth natural size, After Frank, 
Fu;. 361.— Multicellular hairs ol edelweiss, MagnifU d about 50 diam.— After Kerner, 
Fir.. 362. — Silky unicellular hairs ol Convolvulus Cntorum. Magnified about $" 

ili.1111 Ml. 1 K( ii" 1 



3 22 



PLANT LIFE. 



--:' : \ ' 



bluish-white powder, which can be readily wiped off with the 

ringers, as from the surface 
of fruits, such as plums or 
grapes, the leaf of cab- 
bage, or the stalk of sugar- 
cane (fig. 366). The in- 
^ terior layers of the wall 6T 
■ the epidermis are some- 
- — ttmeT'coivverted into rhu- 
~~cTTage, which retards the 
evaporation ~rjf — -avuU£.i\__ 
^J£he__ sinking of" the sto- 
mata below the general 




Fig. 363. 



wr 








Fig. 363.- Stellate hairs <>f /h<i/:i 
Thomasii, seen from above. 
Magnified about 50 <li. 

After kerner. 

Fig. 364. — T-shaped hairs of Ar- 
temisia mutellina. Magnified 
about 50 diam.— After Kerner. 

1, . 565 Shieldlike si .<l<--s of an 
1 1 /■:/,., ix "'>■■■ ■• 

folia), seen from above. Mag- 
nified about ;•> diam.— After 
Kerner. 



level (fig. 367), their arrangement in pits (fig. 368) or in 
"groTTves (fig. 357), and their restriction to the under side of 
the leaf (fig. 359) may be looked upon as further epidermal 



XEROPHYTES AND HALOPHYTES. 



323 



,ni1-ipfntjnnc tp r^dll^w^yapnrririrm In the leaVCS of SOUK' 

xerophytes the guard cells of the stomata are motile only 
when young, becoming thick-walled and fixed when the leaf 
is mature. The stoma itself sometimes becomes closed, also. 




Fig. 366.- -Portion of a transverse section through a node of sugar-cane, showing rods 
of wax secreted by the epidermis. Magnified 142 diam.— After I »e Bary. 

FlG. 367. — Transverse section of a portion of the margin of a leaf of Aloe socotrina. 
1. thick cuticle; below,, cutinized layers of wall of epidermis,*'/; /, parenchyma 
cells with chloroplasts ; . r. a crystal cell with needle crystals ot oxalate of lime; sp, 

fuard cells of stoma, sunk below surface : .;, intercellular space under stoma. Magni- 
ed about 175 diam. — After Tschirch. 



_{&L- l'he internal tissues of the leaves may be more compact. 
This reduces transpirationby restricting thelil'ea of llie-air 
passa ges. Such dense structure is secured by multiplying 
th e number of the palisaTrrr iTTycrs and by the "Tub re regular 
form of the spongy parenchyma (fig. 359 and ^' 167). 



B. Adaptations for taking up water. 

439. Absorption. — 1. Some plants are adapted to im- 
mediate absorption of moisture in the air or of liquid water 
falling en their aerial parts. Such are. usually, the 
algae, In hens, and mosses which -row in exposed situations. 
2. Certain of the higher plants are furnished with hairs 
adapted to the prompl absorption of rain or dew, e.g., Spanish 



324 



PLANT LIFE. 



moss. 3. < Uhcr plants adapt aerial routs to the absorption of 

moisture from the air, as well as falling water. (See ^ 196.) 
4. Many are surrounded by the bases of dead leaves, which 
act as a sponge for absorbing water, and supply it gradually 
to the stem or younger leaves. Living leaves, sometimes 
singly, sometimes in clusters, form cuplike or tubular struc- 







Fk;. 368.— Portion of a vertical section of leaf of oleander. <■/, epidermis of upper 
face; e/>' , same of lower face with stomata, s, in deep pits with numerous hairs, t: 
pal, palisade parenchyma in two layers; ,r/, spongy parenchyma; //, /;', hypoderma 
adapted to water storage. Chloroplasts shown only in left-hand side of figure. 
Magnified about 175 diani. — After Van Tieghem. 

tures, acting as water receptacles, from which it can be 
absorbed as required. Such adaptations occur chiefly in 
epiphytes. (See" 454-) 5- Many xerophytes develop ex- 
ceedingly long tap roots, which penetrate the soil deeply 
to a permanent water supply. 



XEROPHYTES AND HALOPH YTES. 325 

C. Adaptations for storing water. 

440. 1 . Special cell contents. — The simplest of these adap- 
tations is the presence of mucilage in the cells, arising from 
the cell-wall or developed in the cell-sap of various parts. 
(See *j" 5.) The presence of acids, tannins, and salts perhaps 
aids in the retention of water. 

441. 2. Water-storing tissues. — (a) Fleshy plants, or 
succulents, are those which thicken their parts by the develop- 
ment of an unusual amount of parenchyma, which contains 
a large quantity of cell-sap, and usually much mucilage. 
These thin-walled, mucilage-containing tissues form a reser- 
voir for the storing of water. In such plants the epidermis 
is very strongly water-proofed; the stems are thick, cylin- 
drical, prismatic or spheroidal ; the leaves are wanting, or they 
are thick and fleshy, cylindrical or broad (fig. 369), and 
arranged in rosettes. 

(U) In non-succulents, 
the epidermis itself may 
be greatly developed as 
a water-storing tissue, 
or it may form great 
numbers of bladdery 
hairs which are richly 

supplied with water, as FlG , 3 , 9 ._ A 3Trfto«£k \sL* 
in the well-known "ice- ^SVSSSPfoKS 5*?e3KF 

,i„„, •• ._ ,,.i,;,.k ,k., branches, these become detached and form in- 
piam, on \\nun lilt, dependent plants. About one half natural size.— 

hairs glisten like ice. After Gray. 

In the first case, the epidermis, instead of forming a single 
layer of cells, ma) develop into several layers, the lower ones 
large and thin-walled, as in begonias, figs, and peppers I fig. 
370). The cells immediately under the epidermis sometimes 
become transformed into a water-storing tissue, as in the 
oleanders (fig. 368); or strips of tissue extending from the 




326 



PLANT J.ll-F. 



upper to the lower side of the leaf may act as reservoirs 

of water. 

442. 3. Tubers and bulbs. — These forms of the shoot 
in which the parenchyma is 
abundant and richly supplied 
with water may also be 
counted, in part at least, as an 
adaptation for water-storage. 
443. III. Halophytes. — 
The salt-loving plants arc, 
in most of their characters, 
strikingly similar to the xero- 
phytes. This similarity is to 
be explained probably by the 
difficulty of securing a suita- 
ble water supply. They grow 
near the ocean, upon the 
shores of salt lakes, by salt 
springs, and in the interior 
of the great continents in old 
lake basins in which the salts 
have accumulated by the 
rains. A few of the halophytes 
are trees and shrubs, with 
leathery leaves, but almost all 
are succulents. In habit thev 




Fig 370. — Strip from a vertical section of 
leal "I Peperomia trichocarpa. ./, from 
afreshleaf; w, water-storing tissue, com- ov»n*»rallv In™ nft*»n ,-.-,.,> 1, 

posed of the multiple epidermis of the arC ,^lUiall\ IOW, otUll ( Ucp- 

upper side ;*, chlorophyll-bearing cells; • j, ( jj , fl « ■,,,(! 

s, spongy parenchyma with sparse chloro- " J 6» " ll " nnii\, iksiij aiiu 

plastS and much water. /.'. tin- same after ____, _, 1 , . #.___ ,1,, . ,„ f 1 ^„,. c . 

four days" tr.mspirati,,,, at ,s ,.. C. The nl(>r « <" lesstiailsllH Cllt lea\ CS 

tissue w is much collapsed, the walls being „_ i , __. . 4 i, ii i__ ,, i 

|,l..it.-,i : .also shrunken, but « as before, and stems; the cells large and 

S ified about 5 ° diam - Vfl - Haber - thin-walled, containing com- 
paratively little chlorophyll and abundantly supplied with 
water, with few and small intercellular spaces and the surface 
generally smooth. 



CHAPTER XXII. 

HYDROPHYTES. 

444. IV. Hydrophytes may be divided into three groups : 
i. Slime plants, which grow in the mud or slime at the bot- 
tom of bodies of water. Here belong many algae, especially 

itoms, man\- species of low fungi, and bacteria in great 
numbers. 2. Submersed plants, either free or attached. 
Many alga?, including both the diatoms and the filamentous 
algae, are found floating in the water at various heights, 
sometimes near the surface, sometimes more deeply submersed. 
Since their substance is heavier than water, their capacity to 
sustain themselves depends upon the production of gases in 
the interior of the cells, or upon the presence of gases en- 
tangled among their filaments. A few of the higher plants 
are also found submerged and free, such as the bladder-worts. 
The number of free-floating plants of the larger kinds is 
small compared with those attached. The higher algae, 
moss-worts, fern-worts, and seed plants are usually fastened 
in the mud or to sticks and stones. The thallus of the algae 
is usually profoundly branched and the shoots of the mosses 
are richly supplied with leaves. All of the submerged fern- 
worts and seed plants are characterized by a very thin -walled 
epidermis, the absence of stomata, and the extensive surface 
due to the very profuse branching of the stems or leaves, or 
to the great number of these, or to both. In all cases the 
extensive green surfa< e may be looked upon as an adaptation 
to securing carbon dioxide and the manufacture of sufficient 

327 



328 PLANT LIFE. 

food by means of the weak light in a situation where there is 
no danger from lack of water. 3. Floating or p artly sub- 
mersedpltuils, either free or attached. Many of the Tilamerr^- 
tous algae ahTT~TiTattmis float free at the surface. The chief 
characteristics of the higher floating plants which root in the 
mud are these : their floating leaves are simple, little branched 
or not at all, roundish or elliptical in form, leathery, and the 
surface not easily wetted ; stomata are present only on the 
upper surface, and the leaf stalks are adapted in length 
to the depth of the water in which they grow ; the woody 
tissues are either entirely absent or poorly developed, be- 
cause there is no occasion for the transportation of water, 
nor need of rigidity, since the medium in which they grow 
supports most of the weight. 

445. Light. — Green water plants are limited in their 
distribution by the depth to which light can penetrate water. 
This does not exceed even in pure waters four or five hundred 
meters. No seed plants have been found at a greater depth 
than thirty meters, and few algae at a greater depth than 
forty meters. Plants which are brought up by dredging 
from lower depths than this are usually those which have 
been detached and sunk. 

446. The temperature of the water is very much less sub- 
ject to variation than that of the air, never falling, except 
at the surface, below 0.5 C* 

447. The movements of the water are of much importance 
to plants in bringing air and food materials to them. These 
movements are wave movements, or surf, and currents. 
Plants growing within the limits of wave action are often 
damaged or torn away by the waves. The Sargasso Sea is 
marked by an accumulation of such plants, mainly of brown 

* The minimum temperature of the deeper water is usually stated as 4 
C, but many observations upon Lake Mendota by Birge have shown that 
in winter it falls nearly to zero, even at a depth of eighteen meters. 



HYDROPHYTES. 329 

algas, which have been swept to the quieter parts of the North 
Atlantic by currents after having been detached by the waves. 
Such plants may often live for a long time and may even 
continue their development. 

Plants adapt themselves to currents, such as those in fresh- 
water streams, by their slender form, which is characteristic 
of plants in flowing waters, as seen in filamentous alga? and 
the much divided leaves of higher plants. Currents of water 
act as a stimulus upon certain plants, producing a direct 
reaction in the mode of growth. 

448. The composition of the water affects chiefly the dis- 
tribution of plants, in a manner similar to the presence of 
salts in the soil. In the ocean waters the percentage of salts 
is extremely variable in different regions ; in some places it 
is as low as 0.5 per cent. , while in others it reaches 4 per cent. 
In fresh waters the differences in kind and amount of dis- 
solved salts are chiefly due to differences in the soils which 
the streams drain. 



8 II. ADAPTATIONS TO OTHER PLANTS. 

449. Plant associations. — Each set of external conditions 
brings about the association of certain plants with each other, 
because they have adapted themselves to those conditions. 
The four groups just considered may be looked upon as plant 
societies of the most general kind. Within each of these 
four it is possible to distinguish a number of smaller societies 
determined by a more limited range of conditions. 

Besides these plant associations, however, there are those 
which are determined by the relation of the plants to each 
other, as affording mechanical support, or assistance in the 
work of nutrition. The plant associations of this kind only 
are now to be considered. 



CHAPTER XXIII. 

ADAPTATIONS TO OTHER PLANTS AS SUPPORTS. 

Certain plants serve others as carriers, acting purely as 
mechanical supports. To these supports plants have adapted 
themselves in various ways. In many instances dead objects 
of similar form may serve the same purpose. 'Hie supported 
plants are, therefore, partly independent of the others, though 
in most instances in nature they rely upon living supports. 

450. i. Climbing plants. — Climbing plants are those 
which develop lateral organs, sensitive to contact, which be- 
come recurved or coil about a support of suitable form and 

33" 



ADAPTATIONS TO OTHER PLANTS. 331 

si/o, or form adhesive disks by means of which they cling to 
rough surfaces. These lateral organs are forms either of 
leaves or lateral shoots, and are known as tendrils (figs. 107, 
156). (For their form see % 115, 158; for their action, 
II 266, 293.) 

451. 2. Clambering plants are those which form lateral 
organs not sensitive to contact, and by means of them sup- 
port themselves on adjacent plants. Recurved leaves, shoots, 
and prickles (fig. 115) may serve these purposes. 

452. 3. Twining plants are those which have adapted 
their shoots to winding about a support of suitable size. (See 
If 291.) 

453. 4. Root climbers have adapted their aerial roots to 
attaching the plant to rough surfaces. (See 1" 90.) All of 
these organs are structures belonging to the sporophyte, and, 
therefore, are found only in fernworts and seed plants. 

454. 5. Epiphytes.— Tins name is rather loosely applied 
to those plants which are attached to others for mechanical 
support, and do not derive food from them. All kinds of 
plants have representatives in this group. Algae, diatoms, 
and other small water plants attach themselves to other alga; 
and the higher water plants. Lichens, liverworts, mosses, 
ferns, orchids, bromelias, etc., are abundant upon trees. 
Epiphytes are attached by hair-like rhizoids, or by hold-fasts, 
which apply themselves to the roughnesses or even penetrate 
the outer dead parts, but do not absorb from the living tis- 
sues of the supporting plant either water or food materials. 
The water supply is provided for (1) by adaptations for ab- 
sorbing rain or dew, mists, or even dampness, instantly, either 
by the surface, as in algae, mosses, and lichens, or by means of 
hairs, as in the Spanish moss and other seed plants; (2) by 
adaptations to catch the water in living or dead leaves and 
hold it, either by capillarity or as a vessel, long after pre- 
cipitation has ceased. Many of the simpler epiphytes are 



33 2 PLANT LIFE. 

adapted to become dry without injury, while the larger ones 
are inhabitants of moist tropical regions, where the danger 
of drying is avoided and it is possible to obtain an adequate 
water supply. Their food materials are derived entirely 
from the air and the water which falls upon them, while the 
mineral salts are obtained from the dust which has been 
carried by the air and accumulated upon the surface of the 
supporting plant, or among the mass of dead and decaying 
leaves and other debris about the base of the epiphyte. Or- 
ganic matter from the decay of the older parts may also be 
reabsorbed. 

An adaptation to this mode of life is marked in the repro- 
ductive bodies. Of all epiphytes the seeds or spores are 
either light and carried by the wind ; or the seeds are sticky 
and carried by birds and other animals ; or they are eaten by 
birds and voided upon the trees where they are adapted to 
germinate. 



CHAPTER XXIV. 

SYMBIOSIS. 

455. Living contact. — Not only are different species as- 
sociated through the influence of similar surroundings which 
they find congenial, but certain plants adapt themselves to 
such an intimate relation with others that they live in imme- 
diate contact with them. This intimate association is known 
as symbiosis. When the parties to symbiosis stand to each 
other in the relation of partners, each furnishing certain 
materials or conditions advantageous to the other, the asso- 
ciation is called mulualistic symbiosis or mutualism. When the 
relation of the parties is that of master and slave, one indi- 
vidual deriving advantage from the labor of the other and in 
return furnishing it suitable conditions for existence, the 
association is a form of mutualism known as helotism. Finally, 
when the relation of the parties is that of an unwilling host 
and an unwelcome guest, one individual being fastened upon 
by the other from whose presence it is unable to free itself, 
the symbiosis is called parasitism. (See ^[^[ 51, 52, 53, 
222.) 

A. Mutualism. 

456. 1. Between plants of the same species. — Mutual- 
ism may occur between individuals of the same species. 
Illustrations of this are to be seen in the massing of the 
lower alg?e into colonies, in some of which certain individuals 
may be differentiated from others for the purpose of carrying 
on a function of advantage to the colony. (See 12, 13, 

333 



334 PLANT LIFE. 

20.) In a somewhat similar way certain bacteria are found 
always massed into colonies, constituting a sort of thallus of 




Fig. 371. — A, serpent-like colonies of Chondromyces serpens, composed of numerous 
rod-shaped individuals, B, a, which multiply by fission, />, and secrete a mass of jelly 
which holds them together. A magnified 45 diam.; B, 750 diam.- After Thaxter. 

characteristic outline (fig. 371). In the higher fungi, also, 
the mycelium may be looked upon as a thallus formed by the 
aggregation of many individuals ; for, while it is possible to 
have a mycelium produced from the development of a single 
spore, it is not common. The mycelium is generally the 
result of the union of hyphse (see •; 50) arising from many 
spores. Even in such cases the mycelium may constitute 
a single body, and may give rise to a single fructification. 

457. 2. Between plants of different species. — Mutual- 
ism is more common between plants of different species. It 
takes the following forms: 

458. (a) Lodgers. — The higher plants often shelter 
'various species of lower ones within their intercellular cham- 
bers, or in pockets formed by lobes or bladders of various 
sorts. This relation is especially common between water 
plants and algre. Species of Nostoc live in the intercellular 
spaces of liverworts and duck-weeds, in the cortex of the 
roots of some land plants, and in the bladdery leaf-lobes of 
liverworts. Some species of the higher alga?, also, are 
frequently associated with other species to which they attach 
themselves. That they are not merely epiphytic (see *" 454) 
is shown by the fact that certain species are found only upon 
certain other species, while they do not grow upon other 



.9 YMBIOSIS. 



335 



plants which would furnish them similar external conditions 
(fig. 372). 



LJ % 





A />' 

Fig. 372. Fig. 373. 

Fig. 372. — A portion of a filament of an alga (Ectocarpus^ showing at <( another alga 
[Entoderma Wittrockii) which has embedded itself in the cell-wall. Magnified 480 
diam. — After Wille. 
Fig. 373.— A , a tuft of rootlets of white poplar forming mycorhiza. Natural size. /•'. 
a portion of a transverse section of one of these rootlets, showing the mantle of fungus 
mycelium and the growth of the hyphae also in some of the outer cells of the root. 
Magnified ifiu diam.— After Kerner. 

459. (/') Mycorhiza. — Mutualism between the roots of the 
seed plants and certain fungi is common. Such a combina- 
tion of root and fungus is called a mycorhiza. The fungus 
forms a jacket over the outside of the root (figs. 373, 374), 
taking the place and work of the root hairs by means of 
strands of hyphae extending from the surface of the fungus 
jacket (fig. 374) ; or it grows inside the cells of the cortex 
anil epidermis, forming knotted masses (fig. 375); or it is 
• onfined to certain definite portions of the roots, forming 
upon them swellings from the si/.e of a hazelnut to the size 
of a man's head. The first form is especially common upon 
the roots of the oak, elm, walnut, apple, pear, maple, ash, and 
related trees It has also been found 11)1011 the roots ^\ a 
large number of herbaceous plants. The second form belongs 



336 



PLANT LIFE. 



chiefly to the heaths and orchids. The third form grows 
upon alders, bayberry, etc. 

460. (c) Root tubercles of Leguminosse. — A peculiar case 

of mutualism appears in the bean family between the roots 

and bacteria. The latter produce upon 

the roots small swellings from the size 

of a grain of wheat to that of a hazelnut 

(fig. 376). The presence of these 




*IG. 375- 
Fig. 374.— Tip of a rootlet of beech {Fagus sylvatica) with fungus mantle, the 
hyphae acting as absorbing organs in place of root hairs. Magnified too diam. — After 
Frank. 
FlG. 375. - Mycorhiza of orchids. A, diagram of a longitudinal section of a root ; /, /, 
the cells of cortex filled with hyphae of fungus; i-, stele. Magnified about 20 diam. 
/>', a bit of longitudinal section of root of Ffeottia, near the tap. <■, epidermis ; /, a 
series of cortical cells filled with fungus. Into the ceil a (nearer the tip of root) the 
hyphae are just entering; in the cells above /', recently entered, they have only formed 
a small knot about the nucleus. Magnified about 200 diam.— After Frank. 

bacteria, in away yet unexplained, certainly enables the plant 
to use free nitrogen from the atmosphere, while other plants 
are required to obtain it in combination from the soil. The 
enrichment of the soil by growing clover and similar crops 
upon it and plowing them under is explained by their ability 
thus to accumulate nitrogen from the air. 

461. 3. Between plants and animals. -Mutualism also 



S YMBIOSIS. 



337 



occurs between plants and animals. Various species of plants 
attach themselves to ani- 
mals by which they are 
carried about. The plant 
is thus aided in obtaining 
the materials for food, 
and not infrequently the 
plant conceals the animal 
from another which seeks 
it as prey. In this way 
certain crabs are hidden 
by algne attached to them. 
One of the most striking 
cases of protective m imicry 
is that in which an Aus- 
tralian fish has acquired 
surface outgrowths which 
imitate almost precisely the 
appearance of brown sea- 
weeds, so that, when quiet, Fig. 376.— a young cl 

. , , ,., cles, t, on the roc 

it looks like a stone to Uoff. 

which seaweeds had attached themselves. Thus it often 

escapes its enemies, as does the crab with its 

mask of real seaweeds. 

B. Helotism. 
462. 1. Fungi and algae. — Helotism 
exists between fungi and algae, constituting 

F Hd?S; "Ealnil the bodies known as lichens, in which the 
'• fungus is the master and the alga the slave. 
(See ^[ 54</, and fig. 377.) The same 
fungus may be found enslaving more than 
one species of algae even within the same mycelium. The 
prOtonema of mosses or even the leaves of some small 





enveloping an alga, 
us. Mag- 
nified 950 diam. — 
After Kemer. 



333 



PLANT LIFE. 



plants may be surrounded by a mycelium. The enslaved 
green plants are generally unicellular or filamentous algae. It" 
the latter are the species whose colonies produce voluminous 
gelatine, the texture of the lichen body is gelatinous ; other- 
wise it is tough and leathery. Some 
of the fungi which ordinarily associ- 
ate themselves with alga? to form 

"^^ f /^ff?^'- - i y ' uncns ma y cx ' st *" ree as sa i )r °- 

phytes. The alga itself influences 
the form of the thallus more or less 
profoundly according to its relative 
amount. The same fungus associ- 
ated with different algre produces 
lichens which are described as dif- 
ferent species, or even as different 
genera. 

463. 2. Animals and algae. — 
Helotism exists between animals 
and algae. Various simple animals, 
such as radiolaria stentors, hydras, 
sponges, echinoderms, and worms, 




^ radiolarian iLithn- 
cercus annularis), one of the 
microscopic single-celled animals 
with a siliceous skeleton, .V, 
formed by the outer portions of 
the protoplasm, E, which is sep- 
arated from the internal proto- 
plasm, J, by a perforated cap- 
sule, < ; mi, nucleus; fed, 
threadlike protrusions of the 
protoplasm. Embedded in the 

outer protoplasm, E, are numer- 
ous "yellow cells," Z, each with 
its own cell-wall, nucleus, and 
chloroplasts. These are an alga, 

aXLaAZooxanthellanutricola. enclose algae in their bodies and 

Highly magnified. — After 

Butschli. 



manufacture. The al 
cellular forms which 
division (fig. 378). 



utilize the products of their food 
, r a: thus enslaved are all minute uni- 
multiply within the animal body by 



C. Parasitism. 

464. 1. Fungi. — A very large number of colorless plants 
have adapted themselves to live upon living plants or ani- 
mals which they force to act as their unwilling hosts. By 
the presence of the parasite the normal functions of the host 
or its normal growth or both are more or less seriously inter- 
fered with, so as to produce disease, slight or grave, local or 



SYMBIOSIS. 339 

general, according to the circumstances. Many animals are 




Fig. 379.— Roots of a yellow Gerardia, G, attached to the root of a blueberry bush, B. 
They enlarge at the points of contact and there send haustoria into the host root. 
Natural size.— After Gray. 

thus preyed upon by bacteria and fungi. Most communi- 
cable diseases, such as typhoid fever, diphtheria, and tuber- 




n dodder twining about a hop stem. All but the uppermost coils 
show the groups of wartlike swellings trom whi< h haustoria pi ni trate the host stem. 
Natural 51 v : I ■■ rm nation ol ame. Thi are arranged in ordi 1 

from right to left, tn the lasl ound a suitable support and has 

absorbed all the reserve food in the thicl nd, which has withered and died, 

freeing the plant from the ground. Magnified 1 Vfter Kerner. 



34Q 



PLANT LIFE. 



culosis, are known to be due to the transfer of the parasite 
from the diseased individual to the healthy one. In a similar 
way bacteria live as parasites upon green plants, causing 
disease and often death. The number of bacterial diseases 
among plants is relatively small, for comparatively few bacteria 
have been able to adapt themselves to living in the acid cell- 
sap of plants. The number of diseases of plants due to 
parasitic fungi, on the contrary, is very large. (For the mode 
by which parasitic fungi gain entrance to the bodies of their 
hosts, see % 52.) 

465. 2. Seed plants. — A few seed plants have adapted 
themselves to a parasitic life upon others. Some may be 
reckoned as semi-parasitic, having 
still green leaves and true roots. 
In addition, however, special organs 
are developed for attaching the 
parasite to the roots of other plants, 
from which at least a water supply 
and probably food materials are 
absorbed (fig. 379). Other semi- 
parasites, such as the mistletoe, at- 
tach themselves to the host above 
ground, and have no true roots of 
their own. Some parasitic seed 
plants twine about their hosts, into 
which they send absorbing organs 
by means of which they derive all 
their food from the host. Such is 
the yellow parasitic vine, known as 
dodder (fig. 380, A). These plants 
germinate in the ground, and as seedlings possess true roots, 
but after attaching themselves to the host the lower part 
of the stem dies away so that the true roots are transient (fig. 
380, B). Some root parasites begin to germinate upon the 




Fig. 3S1. — A twig infested with a 
parasitic seed plant {Apodan- 
thes) whose body is hidden un- 
der the bark of the host, through 
whi( h a short branch bearing a 
few scale leaves and a single 
flower bursts. Natural size. — 
After Kerner. 



SYMBIOSIS. 34 l 

ground, but do not pass beyond the first stages of develop- 
ment unless in contact with the root of the host by which 
they are normally sustained. Under these conditions they 
then form a conedike enlargement, which unites with the 
cortex of the host root and penetrates to the stele. From 
this conical stem arise the aerial shoots. Other parasites 
form a network or even a complete hollow cylinder outside 
the wood of the host and under the bark. From this 
curious body the few flowers break through the bark and 
appear upon the surface of the root or stem of the host, quite 
as though they were a part of it (fig. 381). 



§ III. ADAPTATIONS TO ANIMALS. 

CHAPTER XXV. 

ANIMALS AS FOOD, FOES, OR FRIENDS. 

I. Carnivorous plants. 

466. Nitrogen supply. — The ordinary source from which 
green plants obtain nitrogen for the making of their food is 
the nitrogen compounds dissolved in the soil water. Plants 
which live where the soil water contains little or no nitroge- 
nous material are forced to resort to another source of sup- 
ply. Some plants solve the problem by entrapping animals, 
deriving from their bodies the desired nitrogen compounds. 
Such plants are called carnivorous plants, or, since the bulk 
of their catch consists of insects, insectivorous plants. The 
catching of animals is done 

467. i. By pitfalls and traps. — (a) The various pitcher 
plants furnish a fine example of well-devised pitfalls. The 
leaves of these plants have a deep, trumpetlike tube making 
up the body of the leaf; or they carry at the end of a long 
petiole a deep cup with a lid, as in the tropical pitcher plants 
(fig. 382 ; see also fig. 155). The tube is one-third or half 
full of water, in which are always found numbers of dead or 
dying insects. The sides of the tube without art' often made 
attractive by gaudy colors or by lines of sweet secretion, 
which draw both flying and crawling insects. Within, its 
surfaces are either excessively smooth, so as to afford no 

342 



ANIMALS AS FOOD, FOES, OR FRIENDS. 343 



foothold to an insect attempting to crawl out ; or covered by 
stiff, downward-pointing hairs to oppose its passage; or the 
side of the tube is filled 
with thin translucent spots 
through which the cap- 
tives vainly strive to fly, 
while the real opening is 
concealed. By one or 
other of these means the 
prey is prevented from 
escaping, and sooner or 
later is drowned in the 
liquid. In this liquid 
digestive enzymes or bac 
teria quickly dissolve the 
softer parts of the insect 
bodies, and the soluble 
portions are absorbed by 
the leaf. 

{b) The bladderwort, 
which abounds in quiet 
pools, furnishes an ex- 
cellent illustration Of traps Flr - 382— A, trumpet-shaped sessile leaf of Sar- 
racenia variolaris, snowing thin membran- 
(fiUS. 78':, ^84). UnOll m,s windows in the meshes of the veins of 
\ © o 01 o ~tj 1 the hood which arches over the mouth of the 

the leaves are numerous trumpet. /;, cup-shaped petioied leal .if .\v- 

pentkes villosa, with elevated lid and margin 
minute bladders, each ribbed. One-third natural size.— After Kerner. 

with a small opening about which divergent hairs serve as 

guides to the entrance. The entrance is lightly closed by a 

flap of membrane, which is readily lifted by minute water 

animals. After they have passed through the opening the 

membrane drops behind them, ami is stiff enough to prevent 

their escape. Death ensues sooner or later, and absorbing 

hairs on the inner face of the trap take up the nutritive 

materials. 




344 



PLANT LIFE. 



468. 2. By adhesive surfaces. — Animals are also cap- 
tured by adhesive surfaces. These surfaces are covered by a 




■S\ I. ..v -:■ 



m3^ 



.%i. 



Fig. 383. — A bladderwort {Utricularia Grafiana), showing an aerial flower stalk 
carrying an open flower and a second one above from which the corolla lias fallen. 
Some stems bear numerous, finely branched leaves, /■, and others the large bladders, 
/>'. See fig. 384. A shoot of a' smaller species is shown at a, with bladders and 
leu is on same stem. About two-thirds natural size.— After Kerner. 



sticky fluid secreted by numerous glandular hairs, and upon 
these many small insects may be found dead. In many 



ANIMALS AS FOOD, FOES, OK FRIENDS. 345 



cases the softer parts of the insect bodies are digested and 
absorbed. It should be noted, however, that adhesive sur- 




Fig. 384. B Fig. 385- A 

Fig. 384. — A bladder of Utricularia vulgaris, halved lengthwise, with an imprisoned 

crustacean, Cyclops, a to b, opening, with hairs, //, i, about it; b to c, cushion-like 

rim, b-c part cut through, d-e surface on which the flap,./, rests, opening inwards only ; 

g, wall of bladder set with absorbing hairs within and glandular hairs without ; k, the 

stalk (secondary petiole). Magnified 20 diam. — After Cohn. 
Fig. 3S5.— Two leaves of sun-dew I Drosera rotundifolia). A, in expanded position 

showing the tentacles. B, shortly after the capture of an insect. The tentacles on the 

right half are indexed to bring the glandular tips in contact with the prey. Magnified 

z\ diam. — Alter Kerner. 

faces are also merely protective against the visits of unwel- 
come guests, who steal nectar or pollen. (See ^[ 488.) 

469. 3. By move- 
ments of traps and 
adhesive surfaces. — 
Somewhat more 
complex methods of 
capture are exhibited 
by leaves which have 
special movements 
connected with traps 
or sticky surfaces. 
The sundew of our 
swamps has the edges 
and surface of the leaves covered 




-Sgf? 



Fir.. 386.— Cluster of leaves at the base of flower stalk 
of Venus' fly-trap {Dioncea muscf/ula). One-half 

natural size.- Alter Drude. 



r ith many outgrowths, 



346 



PLANT LIFE. 



each of which is tipped by a large gland (fig. 385). The 
clear, glistening fluid, a large drop of which is secreted 
by each gland, is sticky enough 
to entangle even insects of con- 
siderable size, which alight upon 
the leaves. The viscid secretion 
envelops the struggling insect, and 
at the same time the branches of 
the leaves bend slowly inward 
until more and more of the sticky 
glands are thrust upon it. The 
character of the secretion then 
changes. It becomes 
more watery and 
contains ferments 
which soon digest 
the softer parts of the 





Fig 187. — .-/, blooming plant <>f Aldrovandia vesiculosa. Natural size. Vfter 
Drude. B, a single circle ol leaves seen from the center above, slum-inn stalk ami 
two semicircular lobes. Magnified] diam V.fter Caspary. 

Fig. 388. Transverse section through closed trap of A Idrovandia, showing on inner 
face long sensitive hairs and many absorption hairs. Only the central part is three 
layers of cells thick; abroad margin is only one cell thick. Compare appearance in 
''■ fig- :< s 7- Magnified 2<> diam. — After Caspary. 

body. These are absorbed, and play an important part in 
the nutrition of the plant. 

Dioncea (fig. 386) and its water mate, Aldrovandia (fig. 
387), have leaves whose blades are somewhat like a spring 



ANIMALS AS FOOD, FOES, OR FRIENDS. 347 

trap. The blade is two-lobed, with a hinge along the middle 
(figs. 205, 388;. The hinge is in reality a cushion of tissue 
upon the back, which quickly throws the two halves of the 
leaf together when the sensitive hairs on the inner face 
of the trap are touched. The movement is sudden enough 
in Dioncea to catch the slow-flying insect, or, in Aldrovandia, 
the minute water animal. The prey is prevented from escap- 
ing by the interlocking, toothdike lobes along the edges 
of the leaf. Digestion and absorption of the nitrogenous 
materials follow.* 

II. Herbivorous animals. 

470. Protection. — While a really insignificant number of 
minute animals are eaten by plants, a very large number of 
plants find it necessary to protect themselves in some way 
against destruction by browsing animals, insects, snails, 
and slugs. Since the animal world relies for its food 
supply ultimately upon the green plants, it is plain that 
no such protective measures are completely effective. The 
protection, therefore, may be looked upon as a protection 
against extermination rather than against injury. As pro- 
tective adaptations against browsing animals are usually 
reckoned : 

471. 1. Armor, in the form of hard, leathery, sharp- 
edged, woollv, bristly, or sticky parts, especially leaves 
(figs. 361, 362, 364, 389); or thorns (figs. 157, 390), prickles 
( fig. 115), or stinging hairs | fig. 391). 

*Travesties upon these strange methods of nutrition appear periodically 
in newspapers, and plants of remarkable size and forbidding aspect are 
represented as capturing birds, animals, and even men, thai venture into 
their neighborhood. It should be noted, therefore, that in all cases the 
plants which capture animal food entrap only the smaller animal-, scarcely 
any of them, except those caught by the pitcher plants, larger than the 

common house fly. 



348 



PLANT LIFE. 



472. 2. Distasteful or injurious substances, such as 
volatile oils, camphors, acids, tannins, alkaloids, etc. The 
milky juice of plants like milkweeds, which e 

often contain acrid substances, may also be 
protective. 

473. 3. Mimicry. — Certain plants which 
are not distasteful or disagreeable have 
adopted the same form of leaves and stem 
and the general habit of those which graz- 
ing animals have found distasteful. This 

mimicry causes them to be 
avoided, as well as the really 
hurtful ones which they imitate. 





Fig. 389. 



Fig. 390. 



Fig. 389. — Edge of a leaf of a sedge (Carex strii t,i), showing alternate epidermal cells 
pointed and underlaid by two layers of mechanical cells. Magnified 200 diam.— After 
Kerner. 

Fig. 390. — Part of a shoot of barberry in spring showing leaves of preceding year as 
persistent three-pointed thorns, in whose axils the buds are developing into the sea- 
son's siioots. Natural size. — After Kerner. 

Fig. 391. — A stinging hair of the nettle {JJrticd) t in longitudinal section, x, emerg- 
ence in which the single-celled hair abc is sunk below <il<. The knoblike apex < is 
easily broken off because the cell wall just below it is thin and brittle. The oblique 
cutting edge left pierces the skin like a hypodermic needle and some of the acrid cell 
contents enters the wound, causing intense itching. Magnified 60 diam. — After 
Frank. 

474. 4. Ants. — In the tropics particularly, certain plants 



ANIMALS AS FOOD, FOES, OR FN I ENDS. 349 



secure themselves from the attacks both of browsing ani 
inals and leaf-cutting insects 
by encouraging the presence 
of colonies of warlike ants 
upon them and making pro- 
vision for their defenders' 
wants. A very large number 
of species * protect themselves 
in this way. For the ants 
the plants provide (a) nectar, 





Fig. 392. 



Fig J93. 



Fig. 392.-P.it of a section through the cushion («•', fie;, 303I at base ol leal ol ( 'ecropia, 
showing the velvet} hairs with which it is covered, and among them the egg-like 
bodies, rich in proteids and fats, whi< h the ants collect and cany into their nests in the 
interior of the stem. Magnified about mcliam. After Schimper. 

Fig J93 \pr\ ol the hollow stem of a young Cecropia. a, the thin spot above a 
leaf, whii h al lias bei 11 gnawed through by the ants to make their nest in the cavity 
ol the stem : 1 . the I u hion at lias,- ,.1 I, .it si'.ilk where food bodies grow. See fig. 39--. 
Two-thirds natural size. Alter Schimper. 

similar to that secreted in the flower, i.e., a watery solution 
of various sugars, but secreted by nectaries outside the 
flower ; (//) fodder, in the form of hairs (fig. 392), often of 
peculiar form, richly supplied with nutritive substances, 



More- than three thousand arc listed by Delpino. 



;;o 



PLANT LIFE. 



growing from special parts of the surface, which are regularly 
eaten by the ants and grow again, so that a constant supply is 
at hand; (c) divel/ings of various sorts. Certain plants have 
the stems hollow throughout, with special modification of the 
structure at certain spots, so that an entrance to these hollows 
may be readily made (fig. 393). In others, portions of the 
internodes are much enlarged and hollow ; sometimes only 
the internodes in the region of the flower clusters are thus 
transformed. In other plants chambers are produced by the 
bladdery enlargement of the under part of the leaf near the 
midrib (fig. 394). In some acacias the stipules are developed 



as massive thorns, which 




the ants inhabit. 

475. Domatia. — Somewhat sim- 
ilar dwelling places, though less 
perfect, are provided by many 
plants for the mites. These dwell- 



lii 



r 




Fig. 304. 



395- 



Fk;. 394. — Under side of the base of the leaf blade of Tococa lancifolia, showing 
bladder on each side of midrib, each with entrance at a, a. Natural size. (?)— After 
Si lumunii 

Fig. 395— Domatia on under side of leaves. A, between midrib and laterals of 
Psychotria. 8, between midrib and lateral of the linden ( Tilia Europaa). Magni- 
fied about 5 diam.— After LundstriSm. 



ing places are in the form of minute shelters usually upon the 
under side of the leaves. They are generally formed by hairs 
roofing over an angle of the veins, or by various outgrowths, 
folds and pits (fig. 395). Their significance is not at all 
clear. 



ANIMALS AS FOOD, fiOES, OR FRIENDS. 35 1 

476. 5. Crystals. — Plants protect themselves against soft- 
bodied animals, such as snails and slugs, by means of the 
sharp-pointed crystals which are present in the leaves of 
many species. According to Stahl, all tissues containing 
these crystals are avoided by such animals, but will be readily 
eaten by them after the crystals are removed. 



II. REPRODUCTIVE ADAPTATIONS. 

CHAPTER XXVI. 

PROTECTION AND DISTRIBUTION OF SPORES 
AND SEEDS. 

The present knowledge of reproductive adaptations among 
the flowerless plants is very imperfect, though probably many 
exist. This chapter must, therefore, discuss chiefly the 
adaptations in the more complicated reproductive structures 
of seed plants which have been most studied, with only 
incidental allusions to such arrangements in the lower plants. 

I. Protection against bad weather. 

477. By movements. — Spores unfitted to resist low tem- 
peratures or wetting must be protected from rain, cold, and 
similar conditions. When nectar is secreted in the flower as 
an attraction to insects it is liable to be washed out by rain 
unless access of water to the interior of the flower is pre- 
vented. To avoid these dangers, many plants upon the 
approach of unfavorable weather bend their leaves so as to 
close the flower (fig. 396), or arch the stalk so as to turn the 
blossom into such a position that the rain or snow will not 
reach the sporangia or the nectaries. These movements of 
the leaves and stalk are combined in various ways to meet 
the needs of each particular form. All of them are growth 

352 



DISTRIBUTION OF SPORES AND SEEDS. 353 

movements, brought about by variations in light and tem- 
perature, which act as stimuli. (See ^| 286.) 

II. Adaptation to distribution of spores. 
The fact that spores are found in every group of plants 
from the lowest to the highest makes it probable that a great 




Fig. 396. ''"■ 3^7 

Fig. 396.— A, flower of California poppy (Eschscholtzia), opened in sunshine ; /•'. the 

same, closed in wet weather. Natural size. -After Kerner 
Fig. V17. A, aerial liypha of Pilobolus crystallinus, with sporangium. The liypha is 

swollen beneath the sporangium and very turgid. />'. the same with sporangium torn 

off at base and being shot away by the violent escape of the mucilaginous contents uf 

the hypha. Magnified about lodiam. After Kerner. 

variety of ways will have been adopted by plants to secure 
their distribution. The more important ways may be grouped 
as follows : 

478. 1. By turgor and tension. — Among the fungi, spores 
are often projected from the spore case by the pressure upon 



354 



PLANT LIFE. 



it of neighboring cells, increasing until the sporangium 

ruptures suddenly ami the spores are shot out like projectiles. 
In some cases the whole sporangium is thrown off in this 
fashion, often to the distance of a meter or more (fig. 397). 




Fig. 



B 

Fig. 398. 

Fig. 398.— A, a fly killed by the fly fungus {Empusa Muscce), stuck to wall by hypha 
and surrounded by'a halo of the spores. Two-thirds natural size. B, hvph.v projecting 
into the air from the body of the fly, from whose tips spores are being shot off. 
Several are shown in various stages of development. The turgor of the enlarged end 
of hvpha finally ruptures the atta< hment ol the spore and it is shot off surrounded by 
the mucilaginous contents which cause it to adhere to any object struck. Magnified 
200 diam. "" C, a spore enveloped in mucilage. Magnified 420 diam — After Kcrner. 

Fig. 399. — A, spore chain from a fructification {acidiuni) of the cranberry rust 
(Calyptrospora). s, s, mature warty spores separated by an intermediate cell, w, 
which has arisen by the division of the spore fundament by a transverse wall into a large 
upper and a small lower cell. The upper becomes the spore and the lower thi 
mediate cell which elongates, loses its contents, and dies ; its wall becomes mucilagi- 
nous and so loosens the spores. Magnified 420 diam.— After Hartig. B, three spores 
at tip of an acropetal chain ; the terminal spore therefore smallest A disjunctor, </, 
has been formed between the layers of the partition wall and lias forced them apart 
The white area between two lowest shows area formerly connected. ;/, nuileus. 
Magnified 520 diam.- After Woronin. 

The fungus which attacks and kills house flies in summer 
casts off the single spore from the end of the stalk carrying 
it by the bursting of the end of this stalk through excessive 
turgor (fig. 398). With the spore goes the contents of the 



DISTRIBUTIOX OF STORES AiYD SEEDS. 



355 



stalk, so that it is surrounded by a mass of mucilage, thus 
enabling it to adhere to any object which it strikes. 

Filaments carrying the spores often twist upon drying 
and thus jerk off the spores ;is they suddenly slip past some 
obstruction. When spores are produced in chains, either 
the walls of a special cell or a layer of the cell-wall between 
them may act as a separator by its alteration into mucilage 
(A, fig. 399). In some cases the spores are wedged apart by 
the secretion, between the layers of the wall joining them, of 
a cellulose plug which gradually elongates into a slender 
spindle to whose tips the spores are so slightly attached that 
the lightest breath carries them away (B, fig. 399). The 
elaters of the liverworts (fig. n and c 321) serve in some 
cases to sling out the spores when the capsule bursts ; in other 
cases, as in Marchantia, they entangle the spores, insuring 
gradual and preventing too sparing distribution. The teeth 
around the mouth of the capsule of mosses serve to distribute 
the spores at opportune intervals, instead of having them 
emptied out all at once. In some mosses the teeth are erect 
or recurved when dry, but upon being moistened they arch 
over the mouth, thus 
forming a nearly closed 
cover (fig. 400). < hints 
have the teeth arched 
over the mouth when 
dry or permanently fas- 
tened together by their 
tips, thus narrowing the 
opening and allowing 
the spores to sift out 
between them. In some 
cases the teeth, by their 
form and hygroscopic curvatures, serve to sling out the spores 
to a short distance. In many ferns the annulus of the spo- 




Fig. 4<>" Capsules "i .1 m<.ss [Grimmia) afier 
fall of lid. .-J, teeth erect when dry. leaving cap- 
Bule widely open ; /•'. the same in damp weather. 
Magnified about 10 diam. After Kerner. 



356 



PLANT LIFE. 



rangium tends to straighten itself upon drying, thus rupturing 
the sporangium. After bending backward for some distance 
until the tear gapes wide, it suddenly straightens and hurls 
the spores to a considerable distance (fig. 4or). 




Fig. 401.— Sporangia of the male fern (Aspidium Filix-mas) scattering the spores. 
A, closed; A', burst by the drying of the annulus ; (', the annulus after becoming 
strongly recurved is just returning to a nearly straight form and the spores are thereby 
being hurled toward />'. Magnitied about 65 diam. — After Kerner. 

479. 2. By water. — In perfectly quiet water, distribution 
of spores depends solely upon their own motor organs. Only 
zoospores (see ^| 306) are so furnished. For these a film of 
water is sufficient, and they may swim some distance over 
what appear to be merely moist surfaces. Most of the algae 
and fungi living in water form zoospores. Their production 
is often controlled by external conditions, the formation of 
new individuals being thus provided for when the old are 
threatened with destruction. 

In flowing water and by currents, non-motile spores are 
readily distributed. Even such relatively heavy spores as 
the resting spores of algae may be carried long distances by 
water currents. The microspores ( pollen) of aquatic seed 
plants are sometimes carried to the stigma by water currents, 
as in Vallisneria | fig. 402). 

480. 3. By air currents. — Spores may be readily carried 
by the air on account of their small size and their ability to 



DISTRIBUTION OF SPOKES AND SEEDS. 357 

withstand dryness. Must spores float in the air for some time 
like dust particles, and the slightest current is adequate to 
lift many and carry them along. Spores of most non-aquatiG 




Fie. 402.— Pollination of eel-grass (I'allisneyia spiralis}. The large flower is a pis- 
tillate one. with stigmas .'ringed on under side. About it are floating staminate flow- 
ers in various stages of development, having broken from submersed stems which 
bore them. The ones on the right and left have the boat-shaped perianth lobes turned 
back, stamens mature, and pollen exposed ; one has floated so that the pollen is 
brought into contact with the stigma of the pistillate flower. Magnified 10 diam. — 
After Kerner. 

fungi, mosses, and fernworts are distributed by air currents. 
The microspores of some seed plants, especially the common 
forest trees, are carried in this way. 

481. 4. By animals, especially insects. — It is the seed 
plants, particularly, which have adapted themselves to the 
distribution of spores by this means. The development of 
the male plants in this group must be completed in tin- 
neighborhood of the female plants, tor the reason explained 
in ^[ 386. The microspores must, therefore, be carried to 
the ovules of gymnospenns or to the stigmas of angiosperms 



35 8 PLANT LIFE. 

and lodged there. It has been clearly shown not only that 
adaptations for securing this result have been developed, but 
also that there have arisen various ingenious adaptations to 
sec ure cross-polli nation and to prevent close-pollination. 
(See \ 358.) Some of these may be here enumerated. 

482. Adaptations for cross-pollination. — (a) The sepa- 
ration of the stamens and pistils, staminate flowers and pistil- 
late flowers being produced upon the same plant or even upon 
different plants of the same species ; (I>) the early ripening of 
the stamens so that they discharge their spores before the 
stigma of the same flower is exposed or receptive, or vice 
versa; (c) arrangements preventing the pollen from reaching 
the stigma of the same flower, vvhi< h vary according to the 
different modes by which the transfer of the pollen is made; 
(J , the failure of fertilization to occur when close-pollination 
happens. In such cases the pollen is said to be impotent. 
This means that the male plants are either not completely 
formed by it, or that their sperms do not stimulate the egg 
to development. 

483. Adaptations for close-pollination. — But close-pollin- 
ation, even though it results in weaker offspring, is better 
than entire failure to produce progeny. Therefore, some 
plants permit close-pollination in the event of failure to 
secure cross-pollination, while a few have adaptations which 
insure it. Our common violets produce in the late spring 
and early summer in< onspicuous blossoms which do not open, 
containing stamens with few pollen grains. These flowers, 
however, produce seed abundantly, and always by close- 
pollination. Various other species have similar arrange 
ments. 

484. Adaptations to insects.— The adaptations to secure 
cross pollination through the visits of insects are so numerou 
and so varied, and the advantage in the number and weight 
of seeds produced is so marked, that for most seed plants 



DISTRIBUTION OF SPORES AND SEEDS. 359 

cross-pollination must be considered the far more desirable 
process. Flowers are adapted to insect visitors in the follow- 
ing ways : 

485. (</) Food. — They provide for their visitors edible 
substances, such as nectar and pollen,* material for nest 
building, shelters, or breeding places. 

486. (b) Advertisements. — They advertise the presence 
of such attractions in two ways, which are sometimes com- 
bined, and insects accustomed to visit flowers quickly learn 
to know what the advertisements mean. (i) By color. 
Flowers are so colored as to attract notice ; and this is 
further secured by the large size of individual flowers or by 
massing many small flowers into close clusters. (ii) By odor. 
Odors are due to volatile oils, usually in the epidermis of the 
petals or sepals, often curiously localized. Dusk- and night- 
blooming plants often have heavy odors. 

487. (c) Form and position of parts. — Many plants by 
the form of their flower leaves provide landing places for 
welcome visitors. Guides to the location of the nectar, in 
the form of grooves, folds, hairs, lines of color, etc., are 
often present. The form and position of the stamens and 
pistils is often such as to insure the desired transfer of pollen. 
These positions may be permanent or they may be secured 
by movements at opportune times. Among the movements 
are those due to turgor and those due to the presence of 
motor organs. In a very large number of cases, by the form 
of the flower-leaves and the essential organs the plant is 
adapted to visitation by particular insects, and if these are 
not present, or it their access is denied, constant failure to set 
seeds is the result. Thus one may distinguish plants adapted 
to bees, moths, butterflies, flies, birds, or even snails. 

488. (d) Exclusion of unwelcome visitors. — In addition to 

* The microspores are often produced in great excess of the plant's own 

needs. 



360 



PLANT LIFE. 



provision for welcome guests must be enumerated the meth- 
ods of excluding unwelcome guests, which on account of their 
size and habits are unable to bring about the desired transfer 
of the pollen, while at the same time they rob the plant of 
nectar or pollen provided for more acceptable visitors. 




Fk;. 403. — Flower of Cobeea scandens,b&\\eA\ showing tufts of hairs on the base of 
the filaments, of which there are five ; these close the bottom of the corolla cup where 
nectar is secreted against intruders. Three-fifths natural size. — After Kerner. 



(i) Various obstructions with- 
in the flower may render ac- 
cess to the nectar impossible 
to the smaller and weaker in- 
sects, while allowing others 
to reach it. Such obstruc- 
tions are formed by folds, 
hairs, and other outgrowths 
upon the flower leaves or the 
essential organs (fig. 403). 
(ii) Obstructions outside the 
/lower may exclude crawling 

Fig. 404.— Flower of a saxifrage .{Saxi/rapa insects. Such are sticky Slir- 
controversa), protected against invasion J 

by the numerous sticky glandular hairs on f aces an( J hairs (fig. 404), 
the flower stalk, ovulary, and calyx. Mag- v ° ^ T /» 

nified several diam.— After Kerner. nioatS about the Stem formed 

by cup-shaped leaves holding water, or those formed by 

water in which swamp plants grow. (iii) The time of bloom- 




DISTRIBUTION OF SPORES AND SEEDS. 36 1 

ing also prevents the visits of any insects except those flying 
at that particular season. 



III. Adaptations to the distribution of seeds. 

489. After the ripening of the seed various devices and 
forces operate to scatter them at as great a distance as pos- 
sible from the parent, so that the young plants will not come 
into competition with the old ones or with each other. This 
object, which is secured in lower plants by the distribution 
of the spores, can only be attained in seed plants by scatter- 
ing the seed, because the megaspore is not set free ; the ga- 




Fir,. 405.— Elastic valves for slinging seeds. A, fruit of wild geranium (G. /,i/«.r/r,-) 
with 1 11 -i-Msii-m , ,il\ \ I In live 1 arpels surround an elongated torus, from which the) 
break first at bottom ; curling upward suddenly they sling the seed out oi the basal 
part which has cracked along the inner side. B, fruit ol touch-me-not \lmpatiens 
noli-me tangere), one sound, the other bursted 'riK-i.nin.-ls have curled up elasti- 
cally from the base and slung out the seeds. Natural size. Aftei Kemer. 

metophyte is consequently developed within the sporophyte ; 
and the embryo sporophyte is likewise enclosed by the old 

sporoph] te (See ■ .108.) 



362 PLANT LIFE. 

The methods by which distribution is secured may be 

grouped as follows : 

490. 1 . Distribution by tension and turgor. — Some plants 
(e.g., witch hazel) as they ripen the pericarp, alter its tissues 
in such a way that the contained seeds are compressed when 
the pericarp dries, and after it opens they are pinched out 
from the narrowing valves, as a wet apple or melon seed may 
be shot from between the thumb and finger. In others 
(e.g., touch-me-not and cranesbill) the parts of the peri- 
carp shorten on one side until the strain breaks them loose, 
when they become suddenly elastically curled and sling 
the seeds contained to a considerable distance (fig. 405). 
Somewhat similar causes, i.e., curvatures due to unequal 
shrinkage or swelling of the tissues, enable some fruits 
with long awn or bristles to creep over the ground or to 
bury themselves in it when al- 
ternately moistened and dried 
(fig. 406). The pericarp of the 
squirting cucumber is so dis- 
tended by the almost liquid 
pulp surrounding the seeds that 
it ejects the mass through the 
opening formed by its separa- 
tion from the axis. 

491. 2. Distribution by 
water. — In some plants this 
is secured by the fact that the 
fruits open only when moist- 
ened. In such cases the seeds .. , _. ..,.,. 

lie 406.— Pieces mli> which the fruit of 

may be either Washed OUt from storksbill breaks. There are five ol 

J these each corresponding to .1 carpel and 

the opening pods by rain, or arranged on the sides <.i a prolonged 

1 ° ' - torus as in A , fig 405. A, when dry the 

may be loosened in many beak is spiraHy .-..iie.!: a, when moist. 

' - I lie l>asc is hard and very slurp. .Magin- 

other ways. The seeds are Bed about a diam.— After Noll. 

thus set free at the time best suited to their prompt germi- 




DISTRIBUTION OF SPOKES AND SEEDS. 



363 



nation. Some plants, adapted to distribution by water, are 
provided with floats. These floats may eonsist either of the 
enlarged and bladdery pericarp (or some portion of it), or 
of the spongy, air-filled seed coat. The fruits or seeds are 
thus made more buoyant and float upon the surface instead of 
sinking as usual. Naturally, water-loving plants are chiefly 
adapted to distribution in this manner. 

492. 3. Distribution by winds. — Some plants which secure 
their distribution by winds are only lightly attached to the soil 
at maturity, so that they 
are readily uprooted and 
carried bodily, when dry, 
for considerable distances 
by the wind. The transfer 
is facilitated by the incurv- 
ing of the branches upon 
drying, so that the uprooted 
plant is more or less spheri- 
cal in outline, or by the fact 
that the plant is normally 
spherical by the propor- 
tion of the branches. Such 
plants are known as " tum- 
ble weeds.'* Singly or ag- 
gregated in large bundles 
they arc rolled over plains 
and prairies for long dis- 
tances, shaking out their 
seeds as they go, or open- 
ing their fruits when moist- 
ened. Another adaptation 
for distribution by the 
wind is the small size of some seeds. Thoseofsome orchids 
are so diminutive that it takes 500,000 to weigh 1 gram. 




Fig. 107.— Seeds ol an 1 ■'■ > **\ 

with cells ol seed coal bladdery and filled with 
air. These seeds are eje< ted From the < apsule 
by the contortions ol the hairs on its inner 
faces which curve and twist as the moisture in 
the ah varii s. Magnified diam Ifter 



3^4 



PLANT LIFE. 



Such minute seeds are readily blown long distances by 
the wind. Relative lightness is also secured by the con- 
struction of some seeds, which are surrounded by a volu- 
minous coat containing many large air spaces (fig. 407). 
Outgrowths from parts of the seed coat or pericarp also secure 
the same end. In such cases the fall of the fruit or seed 
though the air is so retarded that it may be carried laterally 
some distance by the wind. No seeds, however small, float 
long in quiet air, since buoyancy is derived only from air- 




Fro. 408. — Fruits with wings. A , fruits of ailanthus tree (A . gla miulosus), each carpel 
with double wing. />', truits oi a maple tree, each carpel with a single wing. Natural 
size. — After Kerner. 



containing tissues. A flattened form of the fruit or seed is 
very common, and this form is often exaggerated by the 
formation of wings, i.e., of thin outgrowths from the surface 
(fig. 408). The center of gravity in such cases is so placed 
that the plane of flattening will be nearly horizontal when the 
seed falls. These fruits or seeds sink from 1 to 30 times as 
slowly as the same bodies without the wing. Sometimes spe- 
cialized persistent flower leaves, either corolla or calyx, are 
used for this purpose, as in dandelion and thistle (fig. 409). 



DISTRIBUTION OF SPORES AND SEEDS. 365 

Hairs of the most various origin arc produced in such 
numbers and position as to form either parachutes or tangled 
woolly envelopes to the fruit or sec Is ( figs. 410, 41 1). 




Fig. 41" 



Fig. 409.— Heads of fruits of the dandelion; single fruits falling, exposing common 

torus and involucre. Natural size.— After Kernel . 
Fig. 410. — Fruits of a willow, burst, and allowing the seeds, each with .1 tuft of silky 

hairs (coma), to escape. Natural size. — After Kerner. 

493. 4. Distribution by animals. — To secure this there 
arc two general methods observable. (</) The seed or fruit 
is cither adapted for transport by adhering to the both- of the 
animal ; or (b) the seeds are surrounded by edible parts, and at 
the same time so protected against the digestive juices that 
they may pass uninjured through the alimentary canal. A few 
plants are distributed by animals which collect and hide their 
fruits or seeds (e.g., the squirrels 1. The adhesion of fruitsor 
seeds to animals, especially to those which are provided with 



3 66 



PLANT LIFE. 




-A fruit of Barbadoes cotton, open, exposing the voluminous hairs (commer- 
cial cotton) which clothe the seeds. Natural size. — After Kerner. 




Fig. 



412. 



Fig. 



Fig. 412. — Fruit of Agritnonia, halved; showing torus, carrying calyx and withered 
stamens above, covered with hooks, and enclosing the hard peril irp, with a single 
seed. A pistil which did not mature lies to the right. Compare torus in tig. 288. 
Magnified about 8 diam. — After Baillon. 

FlG. 413. — Fruit of tick trefoil {Desmodium Canadense). A, pods which separate into 
sections, each containing one seed. They are covered with stiff hooked hairs, some 
of which are shown enlarged at />'. A, natural size. />', magnified about 20 diam. — 
After Kerner. 



DISTRIBUTION OF SPORES AND SEEDS. 367 



fur, is generally secured either by surfaces made adhesive by 
the sticky secretion from glandular hairs, or by the develop- 
ment of outgrowths in the form of hooks or barbed prickles 
(figs 412,413, 414,415). A few water animals and wading 
birds distribute seeds which . 
happen to fall into the mud 
by the adhesion of this mud 
to their bodies. 

The fleshy fruits with edible 
parts are usually colored to 
attract the notice of the fruit- 
eating animals. Seeds which 
escape crushing by the teeth or 
grinding in the gizzard are apt 
to be in condition to germi- 
nate when voided. The seeds 
of the mistletoe are separated 
from the pulp of the berry by 
the birds which eat them, Fig. 414. Fig. 4 i S . 

nnrl eriVtiner rr> the* Kill or« FlG ' 4J4-— A, cluster of fruits of Spanish 
aiHl, Sticking tO tile Dill, are needles {Bidens bipinnata). A. a single 
m-i'i„.,1 riff ,-m the> KronoViao fruit enlarged, show in< barbed awns, rep- 
Wipea OH Oil tile Drancnes resenting the calyx lobes, by which it aS- 

nf trpp« whprp thMV rr*>rmi heres - ,l ' animals - A > natural size; A', 

OI trees, Wliere tney germi- magnified 2i diam.— After Kerner. 

n _j. FlG. 415. — Fruit of cockle-bur ( Kanthium 

u <* tCl strumarium), halved, showing two seeds, 

'l'h.> nrl'ii.tQtinn nf nlontc tn the u .PP er " f which usually germinates a 

1 ne adaptation ot plants to NL . ar i ater ,i, an t i le lower. Natural size 
any one of these agents of AfterArthur - 

distribution is likely to be more or less effective with other 
agents. For example, the tufts of hairs which increase the 
buoyancy of the seed in air would be equally effective 
should the seed chance to alight upon water, or they may 
suffice to entangle the seed in the fur of animals. 

494. Adaptations for germination. — Adaptations for dis- 
tribution not infrequently also secure advantage in germina- 
tion. It is important for man) seeds that they be anchored 
to the ground when they have once been transported, so that 




368 PLANT LIFE. 

they may not be subject to further disturbance. Such an- 
chorage is sometimes secured by the transformation of the 
outer layer of cells into mucilage, so that the seed, upon be- 
coming wet, is stuck fast to the soil ; or by the tufts ot hair 
which, once wetted, cling to the surface of the earth ; or by 
barbed bristles and hygroscopic awns which, having become 
entangled among the grass, work a pointed seed body deeper 
by every change of moisture (fig. 406). 

Study of plants in relation to their surroundings, therefore, 
yields the conclusion that these organisms are wonderfully 
plastic, responding either temporarily or permanently to 
every change in conditions. It is greatly to be desired that 
the too common thought of plants as only things to be clas- 
sified may be replaced by the conception of them as beings at 
work, to be studied alive. 



APPENDIX I. 
DIRECTIONS FOR LABORATORY STUDY. 

Part I : Morphology. 

I. ALG^E. 

A. PLEUROCOCCUS 

i. Examine with a lens pieces of bark bearing Pleurococcus 
and similar algae. Note the irregular distribution of the green 
granular heaps of plants. Is there any similarity to the distri- 
bution of higher plants over uncultivated areas? 

2. After soaking a piece of bark for a few minutes, scrape off 
with the nail or a dull knife blade some of the green material, 
spread it as well as possible in a drop of water on a slip of glass, 
cover it with a piece of thin glass, avoiding air-bubbles, and 
examine with a lens. Observe the minuteness of some of the 
specks, which are mostly single plants. The larger ones are 
clusters of plants. 

3. Demonstration. Examine slide under a high power and 
observe the form and color of single plants. Notice many con- 
sisting of two or more cells still joined together, resulting from 
cell division. (If 19, fig. 18.) 

B. NOSTOC or RIVULARIA. 

1. Observe the size and form of the colonies, and the consist- 
ence of the jelly enclosing them. (" 13.) 

2. Crush a bit of a A r ostoc colony or a whole one of Rivularia 
between two glass slips, remove the upper slip, cover with water 
and observe the coiled (Nostoc) or radiating straight filaments 
(Rivularia) embedded in the jelly. (Figs. 13, 14.) 

369 



37° APPENDIX. 



C. OSCILLARIA. 

1. Observe the color of a bit of Oscillaria; contrast it with that 
of Pleurococcus. (•[ n.) 

2. With needles tease out the specimen in a drop of water on a 
glass slip; observe the delicate thread-like form. (Fig. 15.) 

3. Transfer a bit of living Oscillaria to a small glass dish or 
white individual butter plate with a little water; protect it from 
drying up with a cover; 24 hours later observe the position of 
the filaments. (•[ 14.) 

4. Demonstration. Dip a considerable mass of Oscillaria in hot 
water for a moment and put in a white butter plate with as small 
a quantity of water as will cover it. As the water evaporates 
observe the color deposited on the dish at the edge of the water. 

or no 

D. SPIROGYRA. 

If fresh material is available examine a few filaments in a white 
dish for color. If preserved material is used, stain red by 
immersing for a few minutes in eosin (cheap red ink will answer). 

Examine with a lens. Observe: 

1. Length; whether broken or whole; whether with or without 
branches. 

2. The delicate partitions, like white lines, crossing the green 
(or red) filaments, dividing the protoplasm of one cell from 
another. Can the form of the chforoplasts be seen? (Cf. fig. 24.) 
This can be readily seen only in the larger species. (T 25.) 

3. Demonstration. Mount a few fresh filaments in water. 
Show under moderate power the form of the chloroplasts; the 
reserve food nodules; the nucleus. (Fig. 24.) 

4. Examine conjugating specimens with a lens after staining. 
Observe the conjugating tubes connecting two filaments like rungs 
of a ladder (Tf 361); the zygotes or zygospores (^[365) as blackish 
dots in some cells. Are they in one filament only or in both ? 

5. Demonstration. Mount conjugating filaments and show 
the conjugating tubes and zygospores. (If 375, fig. 303.) 

E. CLADOPHORA. 

If fresh material is at hand observe in a white dish; if pre- 
served specimens are used stain for a few minutes in eosin. 
I. How is the plant attached? 



DIRECTIONS FOR LIBOR A TORY STUDY. 3/1 

2. Observe form and particularly the abundant branching. 
Can a single main axis be traced ? How many branches arise at 
one point ? (Fig. 29.) 

3. Demonstration. Kill and fix the protoplasm of some fila- 
ments of Cladophora by placing them in chrom-acetic acid 
(water, 990 parts; chromic acid, 7 parts; acetic acid, 3 parts) for 
1 hour; wash out the acid by placing them in running water 
for several hours (6-24) or in a large dish of water changed 
several times in the course of 24 hours; stain by placing them in 
alcoholic borax-carmine or hematoxylin for several hours. 
Mount in water. Examine with high power of microscope. 
Each segment of the filament will be seen to contain several 
nuclei (more deeply stained than the body protoplasm and the 
numerous chloroplasts), showing the segments to be camocytes and 
not true cells. (1[ 28.) 

F. STONEWORT (Ckara sp.). 

Place the plant in a glass dish with clean water. Set it over a 
black background if preserved (and therefore colorless) material 
is used. If fresh, a white dish furnishes a good background. 

1. From the base of the axis carefully remove the mud by 
washing. Observe the colorless rhizoids. (IT 37-) 

2. In the body of the plant observe (a) the central axis; {/>) the 
whorls of lateral dwarf branches ("leaves") at intervals 
("nodes"); (c) the single lateral axes arising among the 
whorled dwarf branches. (1[ 33, fig. 35.) 

3. Trace the main axis to its tip. Compare the distance be- 
tween whorls toward the tip. How do they stand close to tip? 
Dissect away the outer ones successively. What is within ? 

4. Demonstration. Prepare or obtain a longitudinal section of 
the apex of the axis, and show under compound microscope the 
apical cell and the differentiation and growth of its successive 
segments. (T[ 39, fig. 38.) 

5. Compare the length of the various lateral axes. Compare 
the tip of any of the long lateral axes with that of the main axis. 
What do the observations show as to the duration of growth of 
these ? 

6. Compare the length of old and young dwarf branches. 
Compare their tips with those of either lateral or main axes. 
What do these observations show as to the duration of growth 
of the dwarf branches? Observe the form and distribution of 
the branchlets. Can they continue to grow in length? 



37 '2 APPENDIX. 

7. Hold a bit of the main axis (use decalcified plants) between 
the halves of a piece of pith and with a very sharp knife or a 
razor cut a transverse section of the axis. Mount on a slide in 
water with cover glass, and examine with lens. Observe the 
central cell, surrounded by a row of cortical cells. (Fig. 37.) 

8. Trace the course of the rows of cortical cells by examining 
the surface of the axis with lens. Note the short projecting cells 
which roughen the surface. (If 35.) 

9. Demonstration. If fresh material is available mount a living 
rhizoid in water and show the rotation of the lumpy protoplasm. 

10. On the lower whorled branches observe the black ovoid 
resting spores, surrounded by a paler cortex, with a crown of five 
cells at the free end. Study these on successively higher and 
higher branches, and observe differences in color, and finally of 
shape. What is the form of the youngest (ovary) ? (T[ 389, fig. 
3I3-) 

11. Examine at the same time the spherical spermaries (orange 
or scarlet in fresh specimens) which are found with some ovaries. 
Why are they absent on older branches ? Can any trace of them 
be found? (If 383, fig. 313.) 

12. Demonstration. Mount young ovaries and show the central 
cylindric egg ; the five cortical cells, straight in the youngest, 
spirally twisted in old«r ones, terminated by five crown cells, 
between which the sperms make their way to the egg. 

Mount entire spermary; also on another slide one teased out 
with needles ; show the eight wall cells, united by zigzag edges, 
each carrying a handle-cell on its inner face, from which arise 
numerous filaments composed of disk-like cells each containing 
one sperm. 

G. POLYSIPHONIA (/'. variegata). 

Place a plant in a glass dish over a black or white background. 
Observe 

1. The form of the body and the mode of branching. (Fig. 39.) 

2. The mode of attachment at the base, if specimens are entire. 

3. Demonstration. Mount the tip of one of the branches and 
show the high, dome-shaped apical cell, with segments cut off 
successively from its base, to be later themselves divided 
longitudinally. (If 39, fig. 41.) 

4. Cut a transverse section of a medium sized axis and observe 
the four large peripheral cells, surrounding a central cell; the 
latter to be seen only under compound microscope. (Tf 3S, fig. 40.) 



DIRECTIONS FOR LABORATORY STUDY. 373 

5. On some plants observe that the smaller branches are 
swollen here and there with more opaque contents at these 
points. These are the tetrasporangia. Compare their size as they 
are traced tip-wards. What do you infer as to their origin ? 
(IT 317. fig- 22Q) 

6. Demonstration. Mount tetrasporic branches and show the 
tetraspores. 

The sexual reproduction is so specialized that beginners should 
not be perplexed with it. (See p. 288.) 

H. BLADDER WRACK {Fucus vesiculosa). 

Place plant in a glass dish or a pan of water. Observe 

1. The general form of the body or thallus; its mode of branch- 
ing. (IT 41.) 

2. The thicker central region forming a midrib, with thinner 
wings. (Figs. 42, 43.) 

3. Downwards, the thickening of rib and death of wings to 
form stalk near base. 

4. The lobed attachment disk at base of stalk. 

5. The swollen regions of the wings here and there. Cut into 
one of these and observe that it is a bladder. 

6. The notched tips of some branches ; the enlarged and more 
or less distorted tips of most, forming the receptacles. 

7. Scattered on the thallus minute elevations, from which pro- 
trude through an opening at the top a tuft of fine hairs. These 
are the mouths of the hair pits. 

8. Crowded on the receptacles, larger warts with a hole at top 
and similar protruding hairs. These are the mouths of larger 
pits, conceptacles, which contain the sex-organs. 

Cut two thin transverse sections of the thallus, one through the 
bladder and the other through the general thallus. The latter 
should include a hair pit. Examine them with a lens and observe 

9. In the latter, the denser outer tissues ; the cortical region ; 
the looser inner ones, of elongated threads and much mucilage, 
the medullary region ; the thicker denser midrib ; the form of the 
hair pit. 

10. Note the difference between the structure of the bladder 
and the unswollen wing. Which region is altered to form the 
bladder ? 

Cut thin transverse sections through the center of the recepta- 



374 APPENDIX. 

cles of male and female plants. If another species than Finns 
vesicuhsus is used (e.g., F. platycarpus) both sex-organs will be 
found in same conceptacle. If the sexes were not collected 
separately and marked they can only be recognized after cutting 
sections by the descriptions and figures given. Observe 

ii. The form and size of conceptacles. Compare with hair 
pit. 

12. In male conceptacles, the crowded and tufted hairs, some 
of whose terminal cells are spermaries. (If 381, figs. 309, 310.) 

13. In female conceptacles, the ovaries of various sizes. The 
larger ones are mature. (IT 3S9, figs. 324, 326, 327.) 

14. Demonstration. Mount very thin sections of male and 
female conceptacles or some of the teased out hairs from them 
and show : 

The oval spermaries, filled with rounded sperms. 
The ovaries, young and old ; in the latter, the eight crowded 
and therefore angular eggs, which round off on escape.* 

II. FUNGI. 

A. BLACK MOLD {Rhizopus nigricans). 

Before any white or black dots appear on the mold, examine 
the vegetative hyplm. ("" 48.) These are of two kinds, (a) those 
running over the surface of the bread ; (b) those penetrating it. 

1. Examine a. Lift up a few threads with a needle and mount 
them in water. Study with a lens. Are they white or colorless? 
Why then is the body composed of them (the mycelium, ^[ 50) 
white ? 

2. Examine /'. With needles tease out hyphrc from a bit of 
bread in water ; free them as far as possible from the debris and 
mount. Compare with a. 

After mold has begun to show black dots (sporangia ) examine. 

3. Determine how the branches are placed which bear the spo- 
rangia, i Fig. 49. ) 

4. Compare the white (young) and black (mature) sporangia. 
Can you find the very smallest ones? 

* If fresh material can be obtained demonstrate the sperms and eggs after escape from 
spermary and ovary. Expose a plant with mature receptacles which has been in sea 
water (01 1 ; pi 1 cent solution oi sea salt) to the air for a few hours: mount in sea 
water on a slide some of the orange exudation which appears at the mouths of male con- 
ceptacles. The water will be found filled with spei maries from which are escaping 
motile sperms. The same treatment with female plants will demonstrate the eggs. By 
mixing drops of water containing sperms and eggs the process of fertilization maybe 
watched. 



DIRECTIONS FOR LABORATORY STUDY. 3/5 

5. Snip off a few ripe sporangia with scissors, handling them 
cautiously to avoid breaking or tangling them ; mount in alcohol * 
and examine. Crush (if not already broken) and observe numer- 
ous dust-like particles, the spores, which escape. 

6. Demonstration. Mount a full grown but immature sporan- 
gium and show the structure of sporangium with septum grown 
up into it forming the columella ; the spores. (1[ 316, fig. 220.) 

B. WHITE RUST (Cystopus portulaca). 

1. Demonstration. Boil a leaf of purslane for a minute or two 
in s% potassic hydrate. Tease apart the tissues of leaf with 
needles on a slide, mount and show the mycelium of the fungus, 
consisting of tangled hyphae ramifying among the cells of leaf. 

(IT 51. 52.) 

Examine a dried leaf. Observe 

2. The white blisters {spore beets) here and there on the surface ; 
the thin membrane (the epidermis of the leaf) by which they are 
covered ; in older blisters the cracking and final disappearance of 
this skin. (IT 312, fig 210. ) 

3. The white powdery spores which jar out or can be dislodged 
with needle. 

4. Demonstration. Cut a transverse section through one of 
these spore beds and show the close set ends of hyphae producing 
the spores in chains. (IT 313. ) 

5. Cut a transverse section of the leaf or stem, mount and 
observe the numerous dark dots scattered through the tissues of 
the host. These are the resting spores with thick opaque walls. 

6. Demonstration. Show in a similar section the spermaries 
and ovaries, and the various stages in the maturing of the fertil- 
ized egg into the resting spore. 

C. MILDEW {Microsphara Friesii, or Erysiphe communis). 

Examine dried leaf bearing mildew. Observe 

1. The whitish interlacing hyphne on surface of leaf, forming 
the mycelium. (If 50.) 

2. The distribution of the fungus ; does it cover the whole leaf 
or only occur in patches ? Compare the earlier and later gathered 
leaves as to this. 

•Because water will not readily wet them. Replace alcohol as it evaporates j it does 
so rapidly. 



376 APPENDIX. 

3. The pulverulent appearance on the younger leaves, due to 
spores. 

4. Demonstration. Scrape a bit of the mycelium from the sur- 
face of the leaf after moistening it for a few minutes with a 5$ 
solution of potassic hydrate. Mount and show (a) the colorless 
branching hyphae ; (6) the erect branches bearing the spores ; (c) 
the spores. 

7. Examine as before one of the older leaves. Observe the 
yellowish dots scattered over the mycelium, the immature fruits. 
(U 401, fig. 337.) Associated with these the black mature fruits. 
These contain sporangia with spores. (*\\ 317, fig. 223.) 

8. Demonstration. Mount and crush under cover glass some 
mature fruits ; show the sporangia (asci) and their contained 
spores. (Fig. 224.) 

D. CUP-FUNGUS (Peziza sp.). 

1. The mycelium penetrates the earth or rotting wood on which 
the fructification appears and cannot be dissected out. Only the 
reproductive parts (T[ 317) are to be examined. Observe the size, 
shape, and color of the cup. The red and orange cups usually 
lose their color in preserved specimens. 

Cut a thin section from a piece of the cup at right angles to 
inner surface. Mount. Observe 

2. The dense upper layer of parallel hyphae (hytnenium), with 
rows of black specks. The latter are the spores in the long 
parallel sporangia (asci). (H 317, fig. 222.) 

3. The lower layer, less dense, of tangled hyphae. 

4. Demonstration. In a very thin vertical section show (a) the 
hymenium, with paraphyses, asci, and ascospores ; (o) the looser 
lower layers of interwoven hyphae. 

E. LICHEN (Physcia stellaris). 

Soften the plants by soaking them in water for a few minutes. 
Observe 

1. The mycelium, forming a connected leaf-like lobed thallus. 
Compare as many other forms as are available. (*} 54a, fig. 225.) 

2. Compare the color when dry and wet. In the latter condi- 
tion, the mycelium is more translucent and the imprisoned green 
algae show through more plainly. (Figs. 55, 377.) 

3. The tufts of hyphae extending from lower surface to bark, 
the holdfasts or rliidnes. 



DIRECTIONS FOR LABORATORY STUDY. 377 

4. Occupying the central region on the upper surface, the 
round colored disks, apothecia. Compare the form of the younger 
ones nearer the margin. What change occurs as they grow 
older? (1 317, n g- 22 5-) 

5. Here and there, minute black specks, the mouths of sacs 
sunk in the thallus, called spermogouia. 

Cut a vertical section through an apothecium and a part of the 
thallus on each side. Observe 

6. The layers of the thallus; above and below, dense layers, the 
upper and lower cortical layers ; between them, the medullary 
hirer, with green alga distributed unequally through it. 

7. The form of the apothecium : its broad short stalk and 
rim; the convex surface of the disk. Is this more convex than 
before cutting ? How shown ? Why? 

8. The layers of the apothecium; the upper (liymenium) of ver- 
tical parallel sporangia containing rows of black dots, the spores ; 
the second {sub-hymenium) of fine, pale, tangled hyphae; the third 
(medullary layer) with green alga:; the lower cortical layer. (Fig. 
226 ) 

9. Demonstration. In a very thin vertical section of apothe- 
cium show the sporangia (asci) and ascospores; the paraphyses. 

10. Compare apothecium with the cup of Peziza. How are 
they different? Do these differences seem important? (Figs. 
222, 226.) 

F. MUSHROOM (Agaricus sp.). 

1. The mycelium of this plant consists of rope- or ribbon-like 
strands of hypha ramifying extensively in the substratum. The 
fructification only is here studied (Tf 314). Examine this part 
fresh or in water. Observe in a mature one the two parts, stalk 
and cap. (Fig. 216.) 

2. With a sharp long-bladed knife or razor cut the cap and 
stalk lengthwise through center. Is the stalk hollow through- 
out? Or is the central part only of different texture from outer ? 
Determine differences of texture by teasing apart the hyphse with 
needles. 

3. Cut off stalk close under the cap. Turn the latter under side 
up. Observe the radial plates (gills) extending from margin to 
stalk. Do all reach the stalk ? 

4. Examine the young fructifications. Ry cutting them length- 
wise observe the formation of the chamber from whose roof the 



378 APPENDIX. 

gills develop; the floor becomes thinner as the chamber enlarges, 
and finally ruptures, exposing the gills. Does any part of this 
floor (called the veil) adhere to the stalk or the edge of cap on 
mature fructifications ? 

5. If fresh mature fructifications are available cut away the 
stalk and place the cap on a piece of black paper,* gills down, 
resting on the stump of stalk, cover with a tumbler or bell jar, 
and examine after 24 hours the spore print formed by the great 
number of spores which have fallen from the surface of the gills. 

6. Demonstration. Cut a very thin transverse section of a gill 
and show the hymenium covering the surface, with basidia carry- 
ing the free spores. (Fig. 213.) 

7. Compare with mushroom various other fructifications of 
related fungi {Hydnum, Boletus, Polyporus, Clavaria). Observe 
the various forms by which extensive surface is secured for the 
hymenium. (T[ 314, figs. 215, 217, 218.) 



III. BRYOPHYTES. 
A. THALLOSE LIVERWORT {Marchantia polymorph*). 

Examine an entire plant in water. Observe 

1. The flattened horizontal body {thallus) with central line, the 
midrib, and thinner wings on each side. 

2. The notched apex (the apical cell is at the base of this 
notch). (% 59.) 

3. The mode of branching {dichotomous). Examine the tips 
and find one just branched. Do not confuse with notch of apex; 
when a tip branches there will soon appear two notches. Does 
the branch appear on the side of the older thallus, or are the 
branches equal at first ? Are they equal when older? (If 58.) 

4. The green lens-shaped bodies {brood-buds) growing at certain 
spots along the midrib, surrounded by an outgrowth which forms 
a cup-like rim about the cluster. Remove a brood-bud and ob- 
serve its form, especially in full grown ones the two opposite 
notches, the growing points. (1J 362, fig. 290.) 

5. The air chambers {areola) of the upper part of the thallus, 
showing through the skin, best seen in older parts and with a 
lens. What is their form ? Are they all alike ? (If 57.) 

* If the gills are light colored ; if dark colored use white paper. 



D IKE C I 'IONS FOK L A BORA'l 'OK V SI' UD Y. S79 

6. The openings into the air chambers, in the skin over each 
one. 

7. Compare the under surface with the upper. Observe the 
numerous hairs. Discover the difference in place of origin and 
direction of growth of these. (^[ 56.) 

8. Carefully pull off with forceps as many of these hairs as 
possible and notice the dark-colored overlapping outgrowths 
along the midrib, curving outward as they are followed forward, 
attached along their edges. These are the so called "leaves." 

Cut a transverse section of the thallus through a brood-bud 
cup. Observe 

9. The origin of the brood-buds (only the younger still remain- 
ing) over the midrib. 

10. The difference between tissue of upper and under parts of 
thallus. (If fresh plants are available observe especially the 
difference in color.) 

12. Demonstration. Cut a very thin transverse section of the 
thallus. Select a part passing through stoma and show 

(1) The air-chamber; its roof, the skin, with chimney-like 
stoma in center; its sides a vertical plate of cells; its floor, with 
branched filaments of chlorophyll-bearing cells. (Fig. 58.) 

(2) The large-celled colorless tissue forming the lower half of 
section; the sections of "leaves" arising near midrib and con- 
cave towards center. 

The sexual branches are so peculiar and specialized that the 
beginner ought not to be puzzled with them. 



B. LEAFY LIVERWORT (Porella platyphylla). 

1. In what position do the plants grow with reference to the 
substratum ? 

Disentangle carefully a single plant.* Observe 

2. The growing apex ; the dying base; the distinctly dorsiven- 
tral habit. Enumerate the differences between the upper and 
under sides. (*[ 60.) 

3. The mode of branching : a central axis, with lateral 
branches, themselves with lateral branches ; i.e., monopodial and 
bipinnate. (If 65.) 

4. The yellowish or brownish stem, covered with leaves 
unequally distributed. 

* If dry, first soften by placing plants in hot water for a few minutes. 



3^0 APPENDIX. 

5. The two rows of large leaves on the upper flanks of the 
stem. How do they overlap? Turn the shoot over and note a 
third row of small underleaves in the center below ; also right 
and left the lobes of the upper leaves. Determine the form of 
the under and upper leaves. Make an enlarged paper pattern of 
the latter showing how their ventral lobes are arranged. (Figs. 
62, 63.) 

6. Demonstration. Mount a leaf and point out the uniformity 
of cells and their abundant chloroplasts. 

7. Examine male plants* and observe the male branches: 
short, abundant near the anterior end of main and lateral axes, 
with crowded, closely overlapping leaves, the anterior ones often 
pale. 

8. Cut off a male branch ; dissect leaves carefully and observe 
in the axil of each leaf a spherical yellowish body on a slender 
stalk, the spermary. (^ 3S2, fig. 311, B.) 

9. Demonstration. Mount a mature but unbroken spermary 
and show the single layer of cells forming a wall enclosing an 
opaque mass of sperms. If fresh, the spermary may rupture on 
being put into water and the sperms swim about rapidly in the 
field of the microscope. 

10. Examine a female plant. On the under side observe very 
short lateral branches, bearing a pear-shaped tumid sac, the 
perianth. How is it constructed at the free end ? 

11. Examine old perianths; observe partly projecting from 
such the mature sporophyte, consisting of a brown spherical capsule 
on a pale slender stalk (seta). (The capsule is often bursted ; if 
so, determine into how many pieces (valves) it splits.) To what 
is the stalk attached ? (T[ 32, figs. 64, 65.) 

12. Examine successively younger female branches (to be 
found toward the anterior end) and note various stages of devel- 
opment of the sporophyte. Find a young sporophyte, differenti- 
ated into stalk and capsule, but still enveloped by a thin mem- 
brane, formed by the enlarged body of ovary and surmounted by 
a brown bristle, the neck of the ovary. Determine what becomes 
of this membrane {calyptra). 

13. Demonstration. Select the youngest female branch with 
well grown perianth, cut a median longitudinal section, or dissect 
away the perianth, mount, and show the group of several ovaries ; 
some with canal cells in place, others with canal cells disorgan- 

* The sexual organs are bome on different plants. 



DIRECTIONS FOR LABORATORY STUDY. 3^1 

ized making an open canal to the egg, and others, perhaps, with 
an embryo sporophyte in the enlarged body. (1[ 391, fig. 331.) 

14. Demonstration. From a mature capsule mount and show 
spores and elaters. (Fig. II, A.) 

C. MOSS [Mnium cuspidatum). 

Examine plants with capsules attached. Observe the two 
connected plants : 

1. The leafy stemmed plant or gametophyte. (*i\ 55.) 

2. The slender plant attached to its tip, the sporophyte, consist- 
ing of a wire-like stalk, the seta, enlarged above to form the 
hanging capsule. ("IH67, 322.) 

3. Boil for a few minutes in 5 per cent, potassic hydrate, rinse 
in water and gently pull sporophyte until it separates from the 
gametophyte. Observe the smooth pointed end which was sunk 
in gametophyte. If properly separated no sign of tearing can be 
seen. (Fig. 73.) 

Examine gametophyte in water. Observe 

4. The differentiation of the body into stem and leaves. 

5. The brown hairs (r/iizou/s) about the stem, which attach 
plant to ground. Do they branch ? (If 62.) 

6. The strength of the stem ; test it by breaking it with a 
lengthwise pull. Cut a thin transverse section and observe dark 
colored mechanical tissues in outer region. (H 63, fig. 68.) 

7. The form and structure of the foliage leaves : note midrib 
of mechanical cells (test strength); lamina of one layer of cells 
large enough to be visible under lens ; border of mechanical cells, 
some projecting pretty regularly as teeth. (^[64, fig. 69.) 

8. Smaller, scale-like leaves on part of the stem. 
Examine sporophyte with mature capsule. Observe 

9. The slender seta. 

10. The thin yellow inverted capsule, from whose end a piece 
has fallen leaving it open. (T 322, fig. 72.) 

11. About the edge of the capsule a fringe of pointed projec- 
tions, teeth, curved inward, constituting the peristome. Break off 
these outer teeth and notice the pale fringed membrane within, 
forming the inner peristome or endostome. (Figs. 72, 231.) 

12. Among these, or to be pressed out of capsule, many fine 
spores. 

13. Demons/ration. Cut off on a slide the end of the capsule as 
a ring, with peristome attached. Divide this ring into halves. 



382 APPENDIX. 

Holding one half with needle cut off the peristome close to cap- 
sule. This allows the teeth to float away from membrane. Turn 
other half with convex side up, cover all pieces, and show the 
peristome, endostome, and spores. 

Examine young sporophytes of this or other mosses. Observe 

14. The cylindrical form of the embryo sporophyte. 

15. The hood covering its apex and carried up by it until the 
developing capsule forces it off. (If 401, fig. 338.) 

16. The lid which falls off to open capsule. 

17. Examine on young gametophytes the sex organs. Dissect 
with needles the tufts of leaves at apex of stem* and search for 
(a) Transparent oval sacs, the empty spermaries ; and similar 
opaque greenish or whitish ones, in which sperms are still en- 
closed. (1[ 384, fig. 311, B). (b) Flask-shaped bodies, with a long 
neck and short stalk, the ovaries. These may always be found, 
withered somewhat, at the tip of a stem where a young sporo- 
phyte is developing. (IT 391, fig. 331.) 

Numerous hairs, paraphyses, of no known function, may be 
found intermixed with the sex organs. 

19. Demonstration. With dissection as above, mount spermary 
and ovary. Show (a) in spermary, the stalk, the wall, the sperm 
cells ; {b) in ovary, the stalk, body, neck, canal, and egg. 

IV. PTERIDOPHYTES. 
A. MAIDENHAIR FERN {Adiantum pe datum). 

I. The gametophyte. 

1. Observe its shape and size ; the notch at the growing point 
(anterior end) ; the dying (posterior) end ; the thicker central 
region, with thin wings. [*\] 69.) 

2. On the under side, a cluster of rhizoids near the posterior 
end. 

3. Compare this plant with the thallus of Marchantia. 

4. Demonstration. Mount a gametophyte underside up, and 
show (a) among the rhizoids the spherical spermaries ; {/>) nearer 
the apex the chimney-like necks of the ovaries. 

If gametophytes with young sporophytes attached are available, 
observe 

* In some species the male organs form at the apex of the axis disk-like clusters, sur- 
rounded by leaves, the whole reminding one in form of a miniature sunflower-head, 
while the female organs occur in smaller numbers (3-6) in the bud-like clusters of leaves 
at the apex of other stems. 



DIRECTIONS FOR LABORATORY STUDY. 383 

5. That the young sporophyte is fastened to the under side of 
the gametophyte. (U 72, figs. 76-78.) 
II. The sporophyte. 
Taking the underground parts in a dish of water, observe 

1. The slender wire-like roots. How are they branched ? (^[ 91 
ff.) Where are they attached to the stem? Trace an unbroken 
one to the tip. The following points can only be seen on roots 
carefully gathered and cleaned. What difference of color near 
tip? Can you find many fine tangled root hairs? Where present ? 
Where absent? (H 79.) 

2. Demonstration. Cut a longitudinal median section of a root 
tip and show the tetrahedral (triangulai in section) apical cell ; 
the segments cut off from inner faces producing root tissues, 
those from outer face producing the root-cap. (U 77, fig. S3.) 

Cut a transverse section of an old root, mount and observe 

3. The outer brown mechanical tissues (also used for storage). 
(H85.) 

4. The central whitish tissue, chiefly the stele, in which the 
visible openings are the larger vessels. (If 81.) 

5. In what position does the stem naturally stand ? Observe 
its occasional branching H[ 103) ; the surface covered with chaffy 
scales (![ 128) ; the growing apex and dying base. 

6. Its nodes and internodes ; the nodes are indicated by the 
attachment of a single leaf at each ; the internodes are the inter- 
vals between the nodes. How are the leaves placed? (^[ 119.) 

Cut a transverse section of the stem and observe 

7. The outer brown mechanical tissues (also used for storage). 

(IT 129.) 

8. The circular, oval, or C-shaped white tissues, most of which 
belong to the stele. Trace the course of the stele through at least 
two internodes by cutting a series of rather thick (1 mm.) sec- 
tions, observing the mode in which the stele branches to pass out 
into a leaf. Cut also a longitudinal section through the base of 
a leaf stalk and trace course of stele. (H1[ 130, 131.) 

Taking a perfect leaf, dried under pressure, observe 

9. The stalk or petiole, with its branches. Note the mode of 
branching; the petiole divides into two equal'divergent branches ; 
each of these forks, one branch carrying leaflets while the other 
again forks, and so on. (^[1[ 153, 155.) 

10. The hardness of the mechanical tissues at surface of polished 
petiole. 



3^4 APPENDIX. 

ii. The leaflets. Note [a) shape, as to outline and margin, 
comparing basal, median, and terminal leaflets of any branch ; 
(b) the veins, containing branches of the stele ; (<r)the green tissues 
between the veins. (1[ 154.) 

12. Demonstration. Strip off a bit of epidermis, mount and show 
(a) the irregular form of epidermal cells; (/<) the intercellular 
openings with guard cells (stomata). (" w , 165, 166.) 

13. Demonstration. Cut a very thin vertical section of a leaf 
at right angles to veins, and show (a) the upper and lower layer 
of cells forming the epidermis; (b) the green parenchyma cells with 
intercellular spaces; (c) the section of the vein composed of the 
stele with mechanical tissues above and below it. (1T^[ 167, 168.) 

14. At the edges of the leaflets on the under side crescentic 
brown spots, sort. (Tf 323.) 

15. Boil a leaflet for a minute in water. With a needle turn 
back a flap which covers the sorus, the indusium; observe that 
it is a specialized portion of the edge of leaflet. 

16. On the under side of the indusium, a mass of yellowish 
spheroidal bodies, the sporangia. Scrape away most of them and 
notice the relation of their points of attachment to the veins. 

Mount some of the sporangia and observe 

17. Their shape; the stalk by which they were attached. (Fig. 
401.) 

18. The darker ridge, annulus, which serves to burst them 
when mature. (Fig. 401.) 

in. Study the manner of bursting. Tear a bit of indusium from 
a dried specimen previously soaked in water, removing most of 
the sporangia. Allow it to dry while watching it-with a lens, 
illuminating from above. 

20. Demonstration. Mount sporangia and spores and show 
their structure, especially the annulus. 

B. HORSETAIL {Equisetum arvense). 

I. The gametophyte cannot be readily obtained, and differs 
from that of the fern mainly in having erect branches, with the 
sex organs on the upper side and always on separate plants.* 

II. The sporophyte. Taking the underground parts in water, 
observe 

* See Goebel, Outlines of Classification, figs. 210, 211; Campbell, Mosses and Ferns, 
fig. 220; Sachs, Physiology of Plants, figs. 425, 426. 



DIRECTIONS FOR LABORATORY STUDY. 385 

1. The slender roots (all secondary); their places of origin. 
(1" 7°-) (Structure quite like ferns.) 

2. The stem; its nodes and internodes; longitudinal shallow 
furrows and low ridges. 

3. At each node a toothed sheath (representing a circle of 
leaves not distinct from each other), best seen on younger region. 

Cut a transverse section of the stem; mount; observe 

4. A circle of large air-canals, one opposite each furrow. Trace 
these lengthwise in an internode. Do they pass the node? 
(1 129.) 

5. Within the circle of air canals, the tissues constitute the stele. 
Opposite each surface ridge, a cluster of small cells looking 
denser than adjacent tissues. These are the cut ends of the 
vascular bundles. (Tf 131.) 

(If underground stems are lacking make out this structure in 
the aerial ones, which differ mainly in being hollow.) 

Examine one of the flesh-colored aerial shoots in water (fig. 
235, A). Observe 

6. Similar distinction into nodes and internodes. Break the 
stem by a lengthwise pull. Where does it break? There is an 
intercalary zone of growth at the base of internode. (Compare 
leaves, ^[ 169.) 

7. The large sheath at each node, the leaves. Each tooth 
represents a scale leaf. Note relation of teeth to ridges of 
stem and to those of sheath next above or below. (Tf 160.) 

8. The different leaves near apex, separate, but whorled and 
crowded in a cone; these are the sporophylls. (HIT. 324, 325, fig. 
235.) Note the lowermost whorl united and forming a sort of 
collar.* 

Dissect off several sporophylls in a small dish of water and 
observe 

9. Their parts, the stalk, the head ; hexagonal form of head 
due to crowding. 

10. The six to ten thin sacs under the head and parallel with 
stalk, the sporangia. (Fig. 236.) 

11. Tear open a sporangium. Leave the spores in a pile on one 
slide and mount a bit of the wall on another. In the latter ob- 
serve the cells with thread-like spiral thickenings on the walls; 



* This may be considered a primitive periantli (.1353) and gives added reason tor 
calling the whole cluster a Bower. 



386 APPENDIX. 

an arrangement to burst the sporangium when mature. (Fig. 
238.) 

Breathe on the dry mass of spores. Watch the squirming 
movements. 

12. Demonstration. Mount a few spores in water and others 
dry, and show the elaters ; strips of the outer walls of spores, 
loosened but wrapped around spores when moist, straightened 
out when dry. (Fig. 239.) 

Examine the green branched shoots (fig. 235, B). Compare struc- 
ture with other shoots, noting differences. Observe 

13. Profuse branching and the arrangement of the branches and 
branchlets. 

14. Cut a longitudinal section through the base of a branch. 
Observe that the branches arise from the stem above the origin 
of leaves and burst through the sheath. 

15. That the nutritive work depends on the stem, not on the 
leaves, which lack green tissue. 

16. The roughness of the surface. Rub branches on a metal 
surface and observe that they scratch it, on account of silica in 
walls of surface cells. 

C. SELAGINELLA (.V. rupestris). 

I. Gametophytes, male and female, are extremely reduced, 
scarcely bursting the wall of the spores producing them. See 

IT! 384. 392, figs. 315, 333. 

II. Sporophyte. 

Examine in water an entire plant. (If previously dry it should 
be boiled for a few minutes in water.) Observe 

1. The yellow thread-like secondary roots arising at various 
points from the stem. (Structure like fern.) 

2. The branched shoots; note method ; lateral branches arising 
from side of mother shoot, i.e., monopodial branching. 

3. The crowded foliage leaves. Mow arranged ? (See p. 97.) 

4. The sporophylls. Search for ends of branches having leaves 
in four vertical ranks. Compare form of these leaves with foliage 
leaves. Observe 

5. In their axils large yellow sacs, the sporangia ; some con- 
taining 

6. One to three large spores, the megaspores; more abundant 
than similar sporangia containing 



DIRECTIONS FOR LABORATORY STUDY. 387 

7. Numerous small spores, the microspores. Microsporangia are 
usually at tip or base of spike and are often difficult to find if 
material is not collected at proper season. (1H[ 326, 327.) 

V. SPERMATOPHYTES.* 

A. PINE (Pinus sylvestris). 

Examine a shoot showing at least the growth of present year 
and that 01 the preceding. Observe 

1. Two kinds 01 axes : (a) the main axis of the shoot, with un- 
limited growth, now terminated by a conical bud ; (/') the very 
short lateral axes of limned growth, dwarf branches, each bear- 
ing two «to/A-/.'i(-r.i. ("| no, rig. 101.) 

2. The six forms of leaves. Scudy the shape and structure of 
each. (a) the slender green leaves, needles ; (b) the scales closely 
covering the older parts of the stem, in whose axils arise the 
dwarf branches carrying the needle-leaves ,- (c) the thin broad 
scales on the dwarf branches, enwrapping the bases of the needle- 
leaves (best seen about the leaves on the young shoot) ; (d) the 
scales protecting the apical bud (If 160) ; (<•) the two forms of 
sporangium-bearing leaves, sporophylls, in the two sorts of flowers 
(see further 4 and 9). 

3. Dissect the scales carefully from a large terminal bud and 
compare the interior parts with those of the shoot which bears it. 
Can you make out the corresponding members? If not, it is 
because the bud is too young. Use a bud taken from the tree in 
summer or autumn and these points can be seen best. What is a 
bud? (p. 85.) 

4. Examine the sporophylls. Observe the two kinds : (a) 
Numerous oval clusters of yellowish bodies, the micro-sporophylls 
or stamens, about the base of the young shoots (fig. 101), now 
called a staminate flower ; (b) a single cluster of mega-sporoph vlls 
about the apex of one or two short lateral branches arising just 
below terminal bud of a young shoot and extending a little beyond 
it, forming the pistillate flower. (■[*[ 331, 344.) 

5. Study the arrangement of the staminate flowers on the axis. 
Compare the position of each cluster of sporophylls (flower} with 

* In this group the sporophytes only can be studied without the compound microscope. 
tophytes sec demonstration 



388 APPENDIX. 

that of the dwarf shoots on the upper part of the same axis. 
What is a flower? (p. 236.) 

6. Dissect off a single micro-sporophyll (stamen) from one of 
the staminate flowers. Observe the broad short stalk ; the thin 
upturned end ; the two large sacs, sporangia, on the under side. 
Tear open these and observe the innumerable small spores, 
microspores (or pollen grains). 

7. Demonstration. Mount mature microspores in water and show 
(<7) the spore itself (the central body) with two bladdery enlarge- 
ments of the outer wall to secure buoyancy in air ; [b) the immature 
male gametophyte inside, consisting of two cells, the smaller rep- 
resenting the vegetative part (a mere rudiment) and the larger the 
spermary, simple by reduction. (If 385.) 

8. Examine a pistillate flower. Observe that it shows from the 
surface two kinds of leaves: (a) thin ones with toothed edge, the 
so-called bracts ; (l>) thick fleshy ones with a prominent point, the 
carpels. These are probably two parts of one structure, the 
sporophyll, which is deeply divided ; but there is wide difference of 
opinion as to the exact nature of the bracts and carpels. 

9. Dissect out a carpel and observe (</) the broad attachment ; 
(/>) the ridge on the upper side (keel) extending into a prominent 
point ; (c) the two enlargements on the upper side near the base, 
the ovules, and their oblique position. The ovules consist of an 
integument and a sporangium containing a single megaspore. 
Note the opening in the integument (micropyle) at the end nearest 
the base of the carpel, with two prolongations right and left. 
(Fig. 246.) 

10. Examine a year-old cone. Observe the excessive growth 
of the carpels as compared with the bracts. Can you find the 
latter by cutting the cone smoothly lengthwise through the cen- 
ter ? Note the woody texture of all parts. (If 404, fig. 341.) 

11. Dissect out an entire carpel. Observe the obliquely placed 
ovules (Fig. 342). 

12. Cut a thin longitudinal section of the ovules and the carpel. 
Observe the sporangium surrounded by the integument prolonged 
beyond it at the orifice ; inside the sporangium a cavity, the 
interior of the megaspore, now partly filled with the young female 
gametophyte. (Compare fig. 319.) 

13. Demonstration. In a similar section show these parts under 
compound microscope, especially (a) the female gametophyte, 
growing inside the spore which has not escaped from the sporan- 



DIRECTIONS FOR LABORATORY STUDY. 389 

giuni; (/•) microspores lodged about the mouth of integument, the 
spermary often forming a tube. (T| 386.) 

Examine a 2-year-old (mature) cone. Observe 

14. The extreme woodiness of the cone, especially the carpels 
which are spread apart when dry. y\ 404.) 

15. On the upper surface of some carpels, two thin wing-like 
scales, with a seed attached. 

16. Time the fall of winged seed from the extreme height to 
which you can reach. Time its fall after removing wing. How 
will this aid in distributing seed ? (H 492.) 

Bisect a seed lengthwise, parallel to flatter faces. Observe 

17. The firm seed-coat, which is the integument of the ovule 
grown and ripened. 

iS. Enclosed by the coat a white tissue loaded with starch and 
oil, the endosperm, which is the enlarged female gametophyte. In 
the center of this the embryo sporophyte which grew from one of 
the eggs produced by the female gametophyte, after the egg was 
fertilized. Note that the tissues of the sporangium have disap- 
peared, having been crowded and absorbed. (T 403.) 

19. Dissect out the embryo from another seed. Observe that 
it is already differentiated into a slender stem, and six primary 
leaves about its apex. (Fig. 339.) 



B. MARSH MARIGOLD (Caltha palustris). 

1. Examine the roots. Observe (a) their surface, wrinkled 
from shortening; (/') their structure. 

2. Cut a transverse section as in fern; observe that mechanical 
tissues are wanting. 

3. Bisect longitudinally the base of a plant. Observe, as shown 
by the origin of leaves, the variable length of internodes; at 
base the internodes are very short so that leaves are crowded; 
in the middle the internodes are long and leaves distant; above, 
the internodes become shorter until, in the flower, they are not 
developed and the leaves are very much crowded. (^[ 119.) 

Study one of the well developed foliage leaves (*1 150). Ob 
serve 

4. The broad rounded blade with slight branches (teeth) at the 
margin. 

5. The long slender stalk, petiole, gradually passing into 



39° APPENDIX. 

6. The sheathing base, in upper leaves branched to form two 
stipules. 

7. Examine and compare the various forms of leaves: {a) the 
lowest, having sheathing bases without petiole or blade, passing 
gradually into (b) the best developed foliage leaves; (c) these near 
the flowers losing petiole and diminishing blade, becoming bracts; 
(d) the yellow perianth leaves ; (<r) next within these the yel- 
lowish stamens (micro-sporophylls); (/) the flattened pod-like 
green carpels (mega-sporophylls) each forming a simple pistil. 
(11 160, 161.) 

8. Bisect a flower lengthwise. Observe the three sorts of 
leaves, perianth, stamens, and carpels; their relation to each 
other and their insertion separately on the enlarged stem, the 
torus. Separate some from an old flower and note the scars left 
by their fall. (1 330.) 

9. Are perianth leaves similar, or of two sorts? (1 354.) 

10. Dissect off a stamen. Observe the two parts: (a) the slender 
stalk, filament, and (b) the enlarged part, anther. Note in the 
anther the two lobes, each with a shallow groove marking the 
position of the two pairs of sporangia. Tear open the sporangia 
with a needle and observe the innumerable microspores (pollen 
grains) which they contain. Examine a naturally bursted anther 
and determine how they open. (HI 345-348.) 

11. Demonstration. Cut a thin section of an anther from a bud 
and show (a) the four sporangia, in pairs, entirely distinct, and 
the point at which they become confluent as they burst; (b) the 
pollen grains. (1 351.) 

Dissect off and examine a pistil. (1 33S.) Observe 

12. At the apex the roughened area, the stigma (1 336), sessile 
(1 337) upon 

13. The enlarged part, the ovulary (I335). Observe its flat- 
tened form and the groove along one edge. Split it along this 
line, flatten it out carefully and note the ovules attached to the 
edges. (1 343.) 

14. Cut several transverse sections of the pistil and observe the 
thickened edges of the carpel, forming the placenta, to which 
ovules are attached. Compare sections. Are all ovules attached 
to same edge ? 

15. Demonstration. Prepare a longitudinal section of an ovule 
of a lily and show the two integuments; the sporangium, enclos- 
ing the single megaspore, or embryo sac. (H 340, 394.) 



DIRECTIONS FOR LABORATORY STUDY. 391 

Study and compare the flower and leaves of the sweet pea 
(Lat/iyrus odoratus), apple, fuchsia, and garden lily. 

For the study of primary roots and root hairs, primary stem 
and primary leaves, germinate Indian corn, scarlet runner or any 
bean, in clean damp pint- sawdust, and grow until plants are sev- 
eral inches high, watching stages of development. 

For forms of stems examine white potato (tuber); onion (bull)); 
Indian turnip or Cyclamen (corm); morning glory or hop (twin- 
ing); white clover (creeping). 

For structure of stems, study Indian corn (monocotyledon, with 
no secondary thickening), cucumber or pumpkin (dicotyledon, 
with no secondary thickening), and young sunflower (dicotyledon, 
with secondary thickening). Compare transverse sections. 

For lenticels and the formation of periderm, examine the twigs 
of plum, cherry, elder or box-elder. 

For buds examine large winter buds of hickory, horsechestnut, 
or poplar. 

Part II: Physiology. 

1. To show the existence of turgor in the individual cell. (•" 188.) 
Mount a bit of Spirogyra under microscope; observe position of 

chlorophyll bands. Irrigate with 5 per cent, solution of salt and 
note effect. 

(If Spirogyra is not at hand use hairs on stamens of Trades- 
cantia ; or the epidermis, filled with purple cell sap, from the 
under side of the leaves of the cultivated 7"radescantia (" wander- 
ing Jew"); or the hairs of geranium leaves.) 

2. To show effect of turgor of cells on rigidity of young parts <<>//- 
taining no mechanical tissues, t". iSS.) 

Remove carefully a young plant with vigorous primary r<>,»t 
grown in sawdust or sand. Lay in water for a few minutes. 
Note rigidity. Transfer to 5 per cent, salt solution for a few 
minutes. Again note rigidity. What has happened? Remove 
to water again for 15 min. What is the result? 

3. To show the existence of longitudinal tensions of tissues due to 
unequal growth or turgor. (" 259.) 

A. Cut a young internode of elder 10 cm. long, making ends 
as square as possible. Measure accurately. Remove wood all 
around and measure pith. Place pith in an atmosphere satu- 



392 APPENDIX. 

rated with moisture and measure after i hour. Compare meas- 
urements. (If elder is not at hand use young shoots of grape, 
wild or cultivated.) 

B. Split a scape of dandelion lengthwise with a sharp knife 
into four strips. Note immediate effect upon their form. Lay 
the strips in water for a few minutes. Observe form. Transfer 
them to 5 per cent, salt solution. What effect? What causes 
these changes of curvature? (The young stems (hypocotyls) of 
castor bean may be substituted for dandelion scapes but are not 
so responsive.) 

4. To show the existence of transverse tensions of tissues due to 
unequal growth. 

A. From a piece of willow or poplar stem separate a ring of 
bark 1 cm. wide, slitting it on one side only, taking care not to 
stretch it. Keep it in a moist atmosphere for a few minutes, 
and then replace it. Does it meet about the wood ? 

B. Cut a slice about 2 mm. thick from the end of a stalk of 
rhubarb. Bisect this and keep the halves for a few minutes in a 
moist atmosphere, then place severed edges together. Do they 
touch throughout ? 

5. To show the location of root hairs and especially their adhesion 
to soil particles. (H 79, 200.) 

Germinate wheat in sand and when seedlings have several 
strong roots dig up carefully; shake sharply in water; note 
where soil clings most tenaciously. Brush away most of this 
with camelhair brush and examine a bit of this part of root under 
a low power of microscope. Observe distortion of root hairs, 
and particles of sand partly embedded in them. 

6. To show excretion of acid salts by roots, (^f 202.) 

Fill a wide-mouthed bottle holding 250 cc. with tap water; add 
2-3 drops of ammonia and several drops of phenolphtalein.* 
If the water does not now remain pink add a drop or two more of 
ammonia. Select a vigorous seedling bean grown in sawdust; 
rinse roots well to remove impurities. 

Cut in two a cork which fits the bottle; in the halves cut two 
corresponding notches of such size that with a little cotton for 
packing the plant will be firmly held. Place the plant with 

* An indicator for acids, colorless when a fluid in which it is dissolved is acid, rose 
pink or darker when alkaline. For use the crystallized phenolphtalein is dissolved in 
alcohol. 



DIRECTIONS FOR LA BORA TORY STUDY. 393 

enough cotton to secure it in the cut cork and set in bottle with 
roots immersed. 

As the plant grows from day to day watch for the dis- 
appearance of color in the solution, whicn will indicate when the 
alkaline fluid has become acid. Arrange a control experiment in 
exactly the same way, but without plant. Surround each bottle 
with opaque shade of heavy paper, to avoid effect of light on the 
roots and fluid. 

7. To show the corrosion of carbonate of lime by the carbonic acid 
excreted by the roots. (T 202.) 

Cover a polished marble slab to a depth of 5 cm. with clean 
sand, in which plant corn or beans. After the plants are 10-15 
cm. high, remove sand carefully and rinse off the marble. 
Examine the surface by reflected light. A little graphite rubbed 
into lines etched by roots will make them more readily visible. 

8. To show root pressure as a factor in the movement of water in 
plants. (Tf 205, fig. 172.) 

Cut off the stem of an actively growing plant (plants of castor 
bean and tomato 25-30 cm. high are especially recommended) 
a short distance above the soil and fasten tightly to the stump, 
by means of rubber tubing, a piece of glass tubing a meter long, 
and about the diameter of the stump. Add enough water to rise 
10 cm. above the rubber connection. Keep roots well watered and 
mark the height of the water in tube from time to time until it 
reaches the top or begins to fall. Does the water rise from the first ? 

A more satisfactory record may be reached by attaching to the 
stump a T-t UDe as shown in fig. 172. To the horizontal arm 
attach a mercury manometer. (A manometer may be readily 
constructed by bending a glass tube, about 5 mm. diameter (3 
mm. bore) and 80 cm. long, upon itself 30 cm. from one end, so 
that it forms a u with unequal legs 3-4 cm. apart. Bend 5 cm. 
of the end of the short leg at right angles, in the plane of the U- 
Tie the legs to a piece of cork between the legs near top, so that 
the tube will not be easily broken by the leverage of the legs <'ii 
the bottom bend.) Fill the space between stump and mercury 
with water. In the third arm insert a short tube drawn out to .1 
slender point to permit the escape of air and extra water. Seal 
this with flame after filling. There must be at least 15 cm. of 
mercury in (J portion of manometer. At beginning mark, with a 
bit of gummed paper, height of mercury in each leg ; measure 
difference at intervals thereafter until mercury begins to fall. 



394 APPENDIX. 

9. To show that water is not absorbed by leaves in quantity ade- 
quate to supply evaporation. (^[ 196.) 

Cut off a vigorous shoot of a plant with abundant foliage ; 
close end of stem with grafting wax ; expose to sunlight until 
slightly wilted ; then immerse it in water. Does the plant recover 
its turgidity ? 

10. To show that many leaves are not wetted by -water. (*[ 210.) 
Immerse various sorts of leaves in water. Does the water wet 

the surface? What is the cause of the silvery reflection of light 
from the surfaces of some ? What relation does this repulsion of 
water have to blocking of stomata by rain? 

11. To show the loss of -water by evaporation. (If 208.) 

Clean and dry the surface of a pot in which a thrifty single- 
stemmed plant is growing ; close the hole in the bottom with a 
cork ; with a brush paint the whole surface with a thick layer of 
melted paraffin. Cut out'a piece of stiff paper which will fit 
around stem and just cover the soil in pot. Using this as a pat- 
tern cut a cover for the soil from a sheet of lead ; slit the cover 
from the central hole to circumference ; adjust it around plant 
and cement all cracks with grafting wax.* Weigh. Weigh again 
at intervals of 24 hours, for 4 days. 

12. To show the variation in the rate of evaporation due to the 
difference in structure of the organ. (^\^\ 209, 438.) 

Compare as shown by shrinkage or by loss of weight, (a) 
Through cork tissue and without it. Take two potatoes ; peel 
one ; expose side by side ; compare day by day. (b) Through skin. 
Compare in same way two apples, (c) Through stomata. Take 
three equal leaves of oleander; of one close the stomata (which 
are on under side only) with a thin coat of grafting wax, or cocoa- 
butter melted and brushed on (taking care not to kill cells by 
having wax too hot) ; coat the upper surface of second in same 
way ; leave third uncovered. Compare day by day. 

13. To show the conditions affecting evaporation. (^T 210.) 
Construct a potometer as follows : Bend the central stem of a 

T-tube until it is parallel with the cross piece. Fit into the lower 
opening of the straight leg a capillary tube 30-40 cm. long, with 
3 cm. of each end bent at right angles to the main part and in 
opposite directions. Into the bent leg fit a shoot of a thrifty 
plant cut off under water, at the same time filling the j-t"be with 

*Or the pot can be set in a tin vessel which it fits and the lead cover luted to this. 



DIRECTIONS FOR LABORATORY STUDY. 395 

water. (To accomplish this bend the shoot to be cut of? so that 
the place of the cut is submerged in a deep pan of water. Fit it 
in tube without exposing cut surface at all to air.) Dip the lower 
end of the capillary tube in water and allow apparatus to stand 
until capillary tube fills with water. Remove the water for a 
moment and allow a bubble r cm. long to enter ; time it as it 
moves between a series of equidistant marks on capillary tube. 
Try the rate under various conditions of light, temperature, and 
moisture acting on shoot. 

14. To show the lifting power of evaporation. (^[ 207.) 

Cut off under water a shoot from a thrifty plant ; fasten it air- 
tight in the end of a piece of glass tubing 30 cm. long, of appro- 
priate diameter, by means of a piece of rubber tubing slipped 
over the end of the stem, taking care not to expose the cut end to 
air. Fill glass tube with water before fitting in plant ; erect the 
whole with lower end of tube dipping in a cup of mercury. Set 
in light and note height of mercury in 1-48 hours. 

15. To show loss of liquid water when absorption is great and 
evaporation slow. 

Grow seedlings of wheat or oats until 5-10 cm. high ; then 
cover with a glass bell for an hour or two. Where do drops of 
water appear ? Why? 

16. To show roughly the path of evaporation stream in woody 
plants. (U 206.) 

A. From a leafy shoot of a woody plant remove a ring of bark 
5 mm. wide. Protect the exposed surface against drying with 
grafting wax. Observe whether the leaves wilt or not, and if 
they wilt, the time required. 

B. With a knife or fine saw cut a little over half through the 
stem of a plant of the same sort used in A ; 1 cm. above this cut 
make a similar one on the opposite side. The two must be so 
placed and of such a depth that all the tissues are severed. Sup- 
port the branch or stiffen it against breaking by bandaging it with 
strips of wood. Make same observations as in ./. Examine the 
pith. Is it alive ? Dues it contain water ? 1 n what tissues, there- 
fore, do you infer water travels to leaves? 

17. To show restoration and maintenance of an interrupted evap- 
oration stream. 

Fit a well wilted shoot into the short arm of an unequal U-tubc 
filled with water to the level of the short end. Allow it to stand 
for half an hour. Does the shoot recover? If not, pour nun ut \ 



39^ APPENDIX. 

into the longer arm until it stands 10 cm. above its level in the 
short arm. Does the shoot now recover turgor ? Why? Allow 
it to stand for some days. Does the level of the mercury change ? 

18. To show in what tissues food most readily travels. (U 235.) 
Girdle as in experiment 16 A a shoot of willow. Cut it off 5 

cm. below ring. Place shoot in water. After some weeks note 
where new roots are formed. Why? 

19. To show the permeability of stomata for air and their com- 
munication -with the system of intercellular spaces. (^T*[ 167, 227.) 

Fasten a leaf with a long petiole air-tight in a rubber cork, 
through which also passes a short glass tube. Fit the cork into 
a bottle holding sufficient water to cover end of petiole. Attach 
a filter pump or air pump to glass tube. Observe whether air 
bubbles leave the end of the leaf stalk. 

Reverse the leaf, so that the blade is immersed, and make same 
observation. Where do bubbles appear ? Is there any difference 
between upper and lower sides? 

20. To show the depth to which light may penetrate green tissues. 

a 231.) 

Take a cylindrical pasteboard or metal tube, closed at one end 
and having a cover which will fit over the closed end. In the 
end and in the cover cut corresponding holes 1 cm. in diam. Mark 
side and cover when in place so that holes can be made to coin- 
cide. On the bottom place a part of a leaf which will cover hole. 
Slip on cover and observe whether light is transmitted through 
leaf. Add successive pieces of leaf until no more light passes. 
What is the color of last light seen ? The examination must be 
made with direct sunlight, and light completely excluded from the 
eye except that which passes through the instrument. 

21. Method for detecting considerable quantities of starch in plant 
organs. (1 233.) 

Boil a few leaves of various plants for a few minutes. Place 
in alcohol at about 6o° C. until all chlorophyll is dissolved.* 
Bring the leaves into a tincture of iodine, diluted to a bright 
brown, for half an hour. The leaves or parts containing starch 
will become bluish, dark blue, or black, according to amount of 
starch present. 

22. To show that manufacture of starch occurs only in cells directly 
illuminated. ("[ 231.) 

* Do not heat over open flame, but set bottle, loosely corked, in a vessel of hot water. 



DIRECTIONS FOR LABORATORY STUDY. 397 

Darken portions of some leaves of a plant previously found to 
show starch in its leaves (sunflower, bean, tomato, or nasturtium) 
by attaching two plates of cork on opposite sides by means of 
two pins driven through both and the leaf. On the afternoon of 
the following day, if sunny, cut off the leaves and test for starch. 
What has become of starch in cells under the cork? 

23. To shozu that oxygen is a by-product of photosyntax, ("]f 250.) 
Collect the gas mixture evolved from a vessel full of aquatic 

plants by inverting over them a funnel to whose tip is connected 
a test tube filled with water to be displaced by the rising gases. 
Keep the plants in sunlight. When the tube is filled, test the 
contents for oxygen by inserting a glowing splinter. 

24. To show the effect of light and temperature on photosyntax, 
using the rate of evolution of oxygen as an index. 

Fasten a shoot of a water plant (Elodea , Myriopkyllum, or Cerat- 
ophyllum) 10 cm. long to a glass rod and immerse in tap water so 
that the cuf end is uppermost. Set in sunlight and observe the 
bubbles rising from the end of stem.* Determine rate at which 
they rise by counting the number given off in a certain short 
time. Continue the observation until the rate is approximately 
uniform. Shade the shoot and determine rate. Return to sun- 
light and determine rate. Put a piece of ice in the water and de- 
termine again. 

25. To show the digestion of starch by diastase. (*[ 237.) 
Powder a handful of malt in a mortar or obtain ground malt. 

To 25 grams of the powder add 100 cc. of water; stir well to- 
gether; allow mixture to stand (with occasional stirring) one to 
two hours; filter; preserve the filtrate. Take 1 gm. of starch 
and rub it up in a dish with 5 cc. water; pour this into gjjj^c. of 
boiling water, stirring as it enters. With 25 cc. of this paste mix 
thoroughly 5 cc. of the filtrate (which contains diastase extracted 
from the malt). Test a small portion of the mixture at once for 
starch by adding a few drops of tincture of iodine, and similar 
portions at intervals of half an hour until starch reaction ceases. 
Taste the remaining paste. Into what has the starch been con- 
verted ? 

26. To show evolution of C0% by respiration of leaves and 
/lowers, (f 239. ) 

* If several bubbles arise at once, remove shoot from water, dry the cut end of Stem 
with filter paper and coat it with a thin layer of grafting wax ; then perforate thi^ wax 
with a line needle point so a.s to offer one ail lot gases. 



39^ APPENDIX. 

Provide a piece of plate glass and a bell jar with ground rim, 
of suitable size to cover a blooming plant growing in a pot. 
Alongside the pot place a shallow dish of baryta-water ; cover 
both with the bell, daubing its edge with vaseline to make con- 
tact with glass plate air-tight. Place in darkness. Note film of 
barium carbonate on surface of water after a day. Conduct a 
control experiment, identical but for the absence of plant. Is 
more or less barium carbonate formed? Why darken? 

27. To show evolution of CO2 by respiration of seedlings. 

Fill a wide-mouthed glass jar or bottle of 1 liter capacity one- 
third full of peas and beans which have been swollen for a day 
in water, then rinsed thoroughly in 5 per cent, formalin 
and again rinsed in water. Cork or cover tightly. After 24-48 
hours remove cover and thrust in a burning match or candle 
attached to a wire. If C0 2 has been produced it will extinguish 
flame. Test also by lowering into jar a vessel of baryta-water. 
If precipitate or film forms it shows presence of C0 2 . 

28. To show the evolution of heat during respiration. (^| 248.) 
Take three-fifths the amount of dry wheat required to fill two 

3-inch flower pots ; swell in water over night ; rinse one half in form- 
alin as above ; kill the other by boiling in water for five minutes. 
Stop bottom hole in pot with a cork; fill one with dead, the other 
with living seeds, and bring the two to same temperature by run- 
ning water through the dead and hot one. Insert a thermometer 
in the center of each mass of seeds ; place both under one box 
or bell jar. Observe changes of temperature for two days.* 

29. To measure the rate of growth in length. 

Construct an auxanometer as follows : Take a board 30 cm. 
square, a common spool, a wheat or oat straw 35 cm. long, and a 
piece of glass tubing 5 cm. long, which will just allow spool to 
revolve easily on it. Close one end of the glass tube by holding 
it in the flame of a Bunsen burner ; when hot spread it enough 
to stop spool from passing over end, by pressing it endwise 
against a piece of iron. With a fine saw cut a section 5 mm. 
thick from middle of spool, thus making a wheel. File a groove 
in edge of this wheel, deep enough to carry a thread. Slip wheel 
on glass tube and fasten it in board near lower left corner so 
deep that spool-wheel will revolve smoothly but have no un- 

* Compare thermometers previously to see that they register alike ; if not ascertain 
the correction. Greater differences in temperature of seeds will be observed if pots are 
surrounded with cotton batting. 



DIRECTIOXS FOR LABORATORY STUDY. 399 

necessary play. On the board, with hole for glass tube as a 
center, mark an arc of 90 degrees. The radius of the arc should 
be a multiple of the radius of wheel. Divide arc into half centi- 
meters. Attach wheat straw to wheel as a pointer. 

To the tip of a growing seedling bean fasten a thread by a slip 
noose. Pass thread over wheel once and to its free end attach a 
light weight — just enough to turn wheel and pointer when plant 
is lifted. Set pointer at o and at intervals read the multiplied 
growth. By taking observations at regular intervals determine 
the rate of growth of stem for a week. What regular variation 
can you discover ? 

30. To show the necessity of respiration for growth. (^[^[242, 245.) 
Germinate a number of beans in sawdust. Select eight with 

straight roots about 2 cm. long. Clean and dry the surface 
slightly by brushing with frayed edges of strips of filter paper, 
taking care not to expose roots so long that they are injured by 
dry air. With a very fine sablehair brush and thick Chinese (or 
waterproof black drawing) ink, mark each root by distinct lines 
into ten spaces 1 mm. apart, commencing with tip. This can be 
done most conveniently by pinning the seedling to a strip of soft 
wood and laying alongside the root a ruler whose graduated edge 
has been blunted by a plane until it is about 2 mm. thick. 

Pin half the seedlings to a strip of soft wood set into a jar 
partly filled with wet sawdust, so that the roots will be vertical 
in damp air. Put the other half into a similar jar and cover them 
with water recently boiled and cooled. After 24 hours, remeasure 
and compare total growth. (See also exp. 31.) 

31. To determine the zone of maximum growth in roots and stems. 
(1 258.) 

A. Observe the four seedlings of exp. 30, whose roots grew in 
moist air. Which spaces grew most? 

B. Mark several upper internodes of a bean plant in a similar 
way, but at 5 mm. intervals. After 4S hours observe how many 
have elongated and which have grown mosti 

32. To show the effect of gravity as a stimulus on roots. (" * 287- 
290.) 

Arrange the marked root of a seedling bean as in exp. 30, ex- 
cept that the root is horizontal, and a pin just above the extrem- 
ity murks its position. After 24 hours observe curvature and 
which spaces have become curved. Compare with those which 
have grown most. 



400 APPENDIX. 

33. To show the effect of gravity as a stimulus on growing regions 
of upright leaves and items. (^[^[ 2S7-29O.) 

A. Support an onion, roots down, in a vessel of water so that 
it is half immersed, until the leaves are about 10 cm. long. Then 
turn it so that leaves are horizontal and observe where curvature 
occurs. 

B. Cover the bottom of a deep dish about 25 cm. long with a 
layer of wet sand, and bank this against one end to the top. Into 
this bank stick horizontally several grass stems having at least 
one node ; cover with a glass plate. After 24-48 hours observe 
curvature. Cut a longitudinal section of the node and observe 
the part of the leaf-sheath in this curvature. 

34. To show the effect of direction of light as a stimulus on leaves. 

(IT 285.) 

Set a potted plant (geranium, sunflower, nasturtium, or mallow) 
in the dark for 24 hours ; then place it before a window, shading 
it so that light reaches it chiefly from one direction. Mark certain 
leaves and record the position of the plane of the blade ; 24 hours 
later observe the position and compare with first. 

35. To show effect of direction of light as a stimulus upon stems 
and roots. (H 285.) 

Grow seedlings of white mustard thus : Tie loosely over the 
mouth of a jelly-glass a double piece of fine bobbinnet; fill vessel 
with tap water to the net, on which place seeds ; set in dark, re- 
placing water as it evaporates, until seedlings are 3 cm. high, 
with roots as long or longer. Then place in a box, blackened 
inside, into which light is admitted, through a hole 4-5 cm. 
in diameter, at right angles to stems and roots. Observe curva- 
tures 24 hours later. 

36. To show effect of intensity of light as a stimulus on certain 
leaves. (^[ 297.) 

Observe the position of the leaflets of white, red, or sweet 
clover, bean, locust, or oxalis at 3 p.m., 6 P.M., at dusk (or after 
nightfall by using a lantern) and at 8 A.M. In the morning darken 
with a box a plant showing these movements. After an hour or 
two, observe the position of leaflets. 

37. To show effect of contact as a stimulus to tendrils. (TJ 293.) 
Stroke with a pencil the concave side of the tip of a tendril of 

passion vine, squash, wild cucumber, or balsam-apple, on a warm 
day or in a hothouse, and observe curvature which follows in a 
few minutes. 



APPENDIX II. 

DIRECTIONS FOR COLLECTING AND 
PRESERVING MATERIAL. 

Those who cannot collect the plants they require can orcki them from the Camhridge 
Botanical Supply Co., 1286 Massachusetts av., Cambridge, Mass. Orders should be 
placed in advance of the collecting season to insure obtaining the material. 

Pleurococcus. — For this and similar one-celled algae, collect pieces 
of shaded fence boards near the ground, or flakes of bark from 
the north side of trees in groves and parks, which show a bright 
yellow-green color. These may be preserved dry. 

Oscillaria. — Search in drippings about watering troughs, city 
gutters where water stands, or any open drain which contains 
organic matter decaying in stagnant water. A glass jar or 
aquarium in which water plants have decayed will usually con- 
tain this plant. It may be recognized by its bluish or blackish 
green color, and often occurs in coherent films or thicker masses. 
It may be obtained fresh at any time of year, either out doors or 
in the laboratory. ■ 

Rivularia. — Collect in midsummer or later the larger water 
plants to whose leaves and stems adhere jelly-like lumps of a 
dirty green color, from the size of a pinhead to 1-2 cm. in 
diameter. The margins of lakes, pools, and slow streams furnish 
the best localities. 

Nostoc colonies form similar jelly masses, commonly larger and 
free floating or attached. Preserve both like the following. 

Spirogyra or Zygnema. — Search in spring or early summer in slow 
streams fed by springs. It will be recognized when in vegetative 
condition by rich green color and slippery " feel." Under the 
microscope the form of the chloroplasts will show the genus. 

401 



402 APPENDIX. 

(See 1[ 25.) When conjugating it often loses the deep green and 
becomes yellowish, and the filaments seem to be double. 

This condition can be recognized under the lens. Spirogyra 
may often be obtained all through the year in pools and springs. 
It should De preserved in the following solution: Camphor water 
50 cc; water 50 cc; glacial acetic acid 0.5 cc. ; copper nitrate 
2 gm.; copper chloride 2 gm. 

Cladophora. — Species of this genus may be found attached to 
sticks and stones at the edge of lakes or pools. It often covers 
these completely with a thick mat of long, yellowish green, 
branched filaments. It may be found throughout the growing 
season. For winter use preserve in same solution as above. 

Chara. — Several species are common in shallow ponds and lakes, 
in water 0.2-1 meter deep, rooting in the mud, often in company 
with Myriophyllum and Ceratophyllum, two seed plants, the latter 
of which may readily be mistaken for it by novices. But these 
plants are usually bright green while Chara is dull or dirty green, 
or even whitish (especially when dry) from the coating of lime, 
which also renders it brittle and harsh to the touch. Careful in- 
spection of its form and a section of the axis at once enables one 
to recognize it. (See figs. 35. 37.) Specimens should be gathered 
when the spermaries on the lower branches (" leaves ")are orange. 
Pull up the plants carefully, wash off as much as possible of the 
mud which clings to the delicate, colorless rhizoids. The basal 
part of the axis should be put in a separate jar from the rest. 
Put a few plants into 2 per cent, chromic acid, and allow them to 
remain 24 hours todissolve off lime with which they are incrusted. 
After pouring off the acid and rinsing them thoroughly, soak 
them in a large vessel of water for 24 hours, changing water 
several times (or allow water to run over them slowly for six 
hours) to remove acid. Preserve in 70 per cent, alcohol. Plants 
may be preserved in formalin or 70 per cent, alcohol, in long 
jars so as to entangle them as little as possible. If brittle from 
alcohol (as they often are) before removing them from jar for 
distribution pour off alcohol and cover with water for a few 
minutes. 

Polysiphonia. — All species are marine, and any common species 
will serve. They are found in reddish brown, feathery tufts 2- 
10 cm. high, on other larger sea-weeds, or on piles and stones, 
about low-water mark. They collapse completely when with- 
drawn from the water. 



COLLECTING AND PRESERVING MATERIAL. 4,0$ 

The plants should be fixed in one per cent, chromic acid (or in a 
saturated solution of picric acid in sea-water) for 12-24 hours, 
washed in sea-water as described for Chara, and hardened in 40, 
60 and 80 per cent, alcohol successively, remaining in each 6- 
24 hours. They may be preserved in the latter. They may also 
be preserved in formalin. 

Fucus. — All species are marine and any one will serve. The 
commonest is Fucus vesiculosus (fig. 42), which may be found on 
rocks between tide marks. It is of olive-brown color, with 
swollen tips to many of the branches, and bladders in pairs along 
the thallus. Plants may be obtained fresh at almost any season. 
Various species of brown sea-weed may be found fresh at the 
fish stores of all large cities, whither they are sent as packing. 

Mucor or Rhizopus. — Saturate a piece of bread with water and 
keep it under a bell jar, in a warm place, for a few days. 
Several species of molds will appear, the most common of which 
is the black mold, Rhizopus nigricans. This may be recognized 
by its white fluffy mycelium, on which arise tufts of erect hyphae 
developing at tips spherical sporangia, at first white, later black. 
These tufts occur at intervals along a stolon-like hypha. The 
same mold may be found on rotting vegetables and fruits, 
especially sweet potatoes and lemons, and may be raised more 
rapidly on bread by sowing spores. It will be followed by the 
green mold, Penicillium glaucum, and often later by other 
species. . Since the plants may be grown promptly, the material 
used should be living. 

Microsphaera or Uncinula or Erysiphe. — Any species of mildew 
will answer. Microsphara grows everywhere on the leaves of 
the cultivated lilac. Erysiphe is abundant on the leaves of blue 
or white vervain {Verbena hastata and V. urticafolia) and many 
Compositae. Uncinula attacks leaves of many willows. About 
midsummer, when the fungus has a white powdery aspect, gather 
leaves and dry them under light pressure. Later, gather leaves 
of the same species showing yellow and black dots (the fruits) on 
the mycelium. Preserve in the same way. 

Cystopus portulacae. — This species is abundant throughout the 
summer on leaves and stems of purslane (Portulaca oleracea) 
which grows in every garden and cornfield. Another s; 
grows in late spring on shepherd's-purse (Cipse//,i bursa-pastoris) 
and another on the pigweeds (AmarantAus sp.). Anyone will 
answer. The species on Capsella (Cystopus candidus) only oc- 



404 APPENDIX. 

casionally forms resting spores in that host. They may be found 
in abundance in the flowers of radish which become much enlarged 
and distorted when this fungus is parasitic thereon. All species 
may be known by the white blisters formed by lifting the skin of 
the host. Preserve in formalin or alcohol leaves and stems of 
host bearing blisters. Some may also be dried. 

Peziza. — The cup fungi grow on earth or fallen rotting leaves, 
twigs or trunks, in woods. The fructifications may be at once 
recognized by their cup-like form. The inner surface of the cup 
is often bright colored, red or orange, brown or black. The 
mycelium is hidden in the substratum. They may be collected in 
spring and summer and preserved in formalin or 70 per cent, 
alcohol. 

Lichens. — Any common foliose species which forms apothecia 
abundantly will answer. A bright gray species with black apo- 
thecia (Physcia stclluris) is abundant on tree trunks, as is also a 
yellowish species with orange apothecia {Theloschistes polycarpa). 
These may be collected at any convenient time, and kept dry. 
Besides these, collect other foliose forms; also species of Cladonia 
growing on the ground, with body much lobed and the apothecia 
coral-red knobs on upright gray stalks; also species of Ustiea, 
clothing the branches of trees with gray-green shrub-like or hair- 
like tufts. 

Mushroom. — Any species with cap and gills will answer. They 
may be found in woods throughout the summer and especially 
in late summer or autumn during a rainy season following 
drought. Only the fructification need be collected. Select a 
small firm species with well defined stalk, cap and gills. Col- 
lect fructifications in all stages of development from young to 
mature. Preserve as soon as gathered in formalin or 70 per cent, 
alcohol. 

Other Hymenomycetes. — Collect fleshy cap fungi with hanging 
points instead of gills {Hydnum, fig. 217), or intersecting plates 
forming tubes {Boletus). Preserve these as mushroom. Collect 
also the woody bracket fungi (Polyporus, fig. 218), which grow on 
rotten trees and fallen limbs, showing innumerable fine tubes 
underneath. Preserve dry. Also the much branched firm- 
fleshed Clavaria (fig. 215). Preserve as mushroom. All will be 
found in damp woods. 

Marchantia. — Common on wet ground and rocks, or even in 
drier places among grass in the shade of walls or fences. It 



COLLECTING AND PRESERVING MATERIAL. 405 

may be recognized by flattish green body about 1 cm. wide and 
5-8 cm. long, attached by silky hairs. At some times it bears on 
the upper surface sessile cups containing green grains, and sends 
up erect slender sexual branches which spread out into flat heads 
6-8 mm. across, some scalloped at edge and some with finger-like 
rays. When cups or sexual branches are present no other liver- 
wort can be mistaken for it. A very similar one, except in these 
parts (Conocephalus conicus) may be distinguished by its larger 
size and larger stomata, looking like needle pricks over the sur- 
face, while those of Marchantia are just visible. It may be used 
for the vegetative parts. Collect in July. Free from dirt as 
much as possible, and preserve in formalin or 70$ alcohol. 

Porella. — Abundant everywhere on the bases of trees especially 
in low grounds or wet bottom lands. It may be recognized by 
its dirty-green pinnately branched shoots, 1-2 mm. wide, with 
crowded overlapping rounded leaves. The plants are always in- 
tricately interwoven. Flakes of the bark may be peeled off with 
a broad knife or chisel, taking care not to tear up the plants into 
too small patches. Collect in summer. Preserve dry, after dry- 
ing under light pressure. Some should be kept in formalin or 
alcohol for demonstration of finer structure of sex organs. 

Mnium. — Any species of the genus will do. The commonest 
species eastward is M. cuspidatum. It is abundant everywhere in 
patches on shady banks and in open woods about the bases of 
trees. It may be recognized by the yellow or orange oval cap- 
sule, thin and irregularly wrinkled when dry, horizontal or pen- 
dent on a stalk 2-3 cm. long. The leaves are broadly oval, with 
fine sharp teeth under lens, and a distinct midrib. When moist 
the leaves are rather pale green, ahd not crowded or overlapping. 
When dry the clump is a dull, dirty green, and the leaves are 
much curled and twisted, expanding quickly when wetted. The 
male and female organs are in the same cluster, at the apex of 
the axis. Under the microscope the species may be recognized 
by the oraitgt- inner peristome with double rows of perforations 
in the membrane below the segments. Preserve as directed fur 
Porella. Almost any similar moss will serve equally well, espe- 
cially the common species of Bryum, 

Equisetum. — The gametophytes are not readily obtainable. The 
sporophytes of the common E. arvinse grows on dry sandy banks, 
often on railroad embankments. The underground stems send 
up in spring (April-May) unbranched flesh colored shoots 5 mm. 



406 APPEXDIX. 

in diameter and 10-25 cm. high, with brown scale-like sheaths at 
the nodes. These shoots terminate in a cone-like cluster of 
sporophylls. Later in the season from the same underground 
stems, grow green much branched shoots, looking somewhat like- 
miniature pines, the main lateral axes being produced in whorls 
at the nodes. Collect both sorts of aerial shoots with under- 
ground shoots and roots attached. Preserve the flesh-colored 
and underground shoots and a few green shoots in alcohol or 
formalin ; most of the green shoots may be dried under light 
pressure between drying paper or newspaper. 

Adiantum. — Gametophytes of any fern will answer. They are 
flat green heart-shaped bodies 2-5 mm. in diameter, attached to 
soil by rhizoids. They may be collected on fern pots or grown 
in greenhouses, or may be obtained from supply company named. 
Especial care should be taken to have some young sporo- 
phytes still attached to gametophytes. The sporophytes of 
the maidenhair fern are easily recognized by the peculiarly 
branched leaf. The stem is wholly underground. Each leaf 
has a slender polished stalk which forks into two equal 
branches ; these fork, one branch of each pair growing straight 
and bearing leaflets while the other again forks in the same way ; 
and so on until 4-8 branches have been formed on each half. 
Collect underground stems and roots, loosening them gently and 
washing off dirt carefully to avoid destroying all root tips and 
hairs. Preserve these in alcohol or formalin. Gather leaves 
when the crescent-shaped fruit dots at edges of leaflets are yel- 
lowish brown (August). Preserve by drying, spreading out 
each leaf to show its mode of branching clearly. 

Selaginella. — A wild species', S. rupestris, grows abundantly on 
dry bare hills and rocks. It forms grayish-green, much branched 
tufts, 3-8 cm. high, with narrow bristle-tipped appressed 
leaves, and resembles in aspect a large rigid moss. Many 
branches are terminated by a sharply quadrangular spike of 
sporophylls, about 1 cm. long. Several exotic species are com- 
monly cultivated in greenhouses and window gardens, where 
they produce sporangia abundantly. Any species will answer. 
Collect the wild plant about July. Specimens may be preserved 
dry or in alcohol or formalin. 

Pinus. — Any species will answer. The Scotch pine is so widely 
planted that it is often easiest to collect. The leaves are grayish 



COLLECTING AND PRESERVING MATERIAL. API 

green, in pairs, 5-10 cm. long; cones small, about 5 cm. long, 
the ends of scales bearing a conspicuous protuberance, long and 
recurved on the basal scales. The Austrian pine, also widely 
planted, has dark green longer leaves (10-15 cm -)» larger cones, 
with no recurved bosses. The flowers are of two sorts and 
should be watched for in spring (May) as new shoots appear. 
The staminate flowers form conspicuous yellow clusters at the 
base of the young shoots, and should be collected as soon as the 
sporangia begin to shed the spores. The pistillate flowers are 
quite inconspicuous, small oval clusters (5-7 mm. long) pro- 
jecting slightly beyond the tip of the young shoots. The tree 
bearing staminate flowers usually bears few pistillate ones, and 
vice versa. Collect shoots bearing each kind of flowers, cutting 
far enough back to include the leaves of the previous year. Pre- 
serve in alcohol or formalin. Collect also year-old and two-year- 
old cones. Preserve the former (green) in fluid; the latter 
(mature) dry. 

Caltha. — This plant is common in wet meadows and swamps 
northward. It is 15-30 cm. high, smooth, with rather coarse 
hollow ribbed stems, orbicular or kidney-shaped alternate leaves, 
with broad clasping base to the petiole, and numerous bright 
yellow flowers 20-25 mm. in diameter, produced for two weeks 
or more in April or May. Gather entire plant; wash the roots. 
Preserve a few plants and an extra supply of flowers and fruits 
in alcohol or formalin. Dry most of the entire plants. 

Lathyrus. — The sweet pea is grown in almost every flower gar- 
den and is known everywhere. Preserve flowers and leaves in 
summer in alcohol or formalin. 

Stems. — The various sorts recommended may be collected at 
any convenient time and preserved in fluid. 

Seeds. — The nmsi useful seeds for laboratory work are Indian corn, 
wheat, buckwheat, castor bean ( Ricinus), white lupine, {Lupinusal- 
dus), scarlet runner (Phaseolus), broad bean {Vicia faba), hemp, 
white mustard. These should be obtained fresh each year, as they 
deteriorate more or less with age. Those which cannot be had 
everywhere (such, perhaps, as lupine, castor bean, scarlel 
runner, and broad bean) may be purchased of seedsmen in Large 
cities. See advertisements in magazines. 

Potted plants. — Such as arc grown in window gardens or all 
greenhouses will suffice. A commercial greenhouse, if accessi- 



408 APPENDIX. 

ble, will raise tomato, castor-bean, bean, and sunflower plants as 
ordered, and will furnish active young plants at any season re- 
quired, in case pupils cannot grow them either at school or home. 
Malt. — Can be obtained ground or unground at any brewery, 
or may be made by sprouting barley until the seedlings appear 
and then drying at about ioo C. 



APPENDIX III. 
APPARATUS AND REAGENTS. 

The chemicals required are so few that in most cases they 
may be most conveniently obtained through local dealers. It is 
desirable, however, to order apparatus from dealers who make a 
specialty of manufacturing or supplying optical, chemical, and 
physical apparatus. Schools are entitled to import such appara- 
tus free of duty, and by doing so through importing firms a large 
part of the cost may be saved. The list is given here for its 
convenience as a summary. The amounts necessary are not 
specified as they vary with the size of classes, and the teacher 
who is prepared to conduct the experiments can readily deter- 
mine how much is needed. 

CHEMICALS. 

Acetic acid. — Used for fixing protoplasm. 

Alcohol. — Large schools should buy in barrel lots free of reve- 
nue tax. For regulations apply to the revenue collector of the 
district in which the school is situated, or to the Secretary of the 
Treasury. 

Ammonium hydrate (ammonia). 

Barium hydrate, — For making baryta water; or this can be ob- 
tained fresh as needed from druggist. 

Chromic acid. — Used in fixing and decalcifying. 

Corn starch. — As prepared for table or laundry. 

Formalin. — This is a 40 per. cent solution of formaldehyde in 
water. Dilute solutions can be prepared as needed. Mosl 
plants require a 10 per cent solution, i.e., formalin 1 part, water 
9 parts. 

Grafting 7cax. — Made as follows : Melt together resin (by 

409 



4IO APPENDIX. 

weight) 4 parts, beeswax 2 parts, tallow i part; mix well; pour 
into a pail of cold water; grease the hands and " pull " till nearly 
white. In using it should be handled with greased fingers to 
prevent its sticking to them. 

Iodine. — Either solid, from which the tincture can be prepared 
by dissolving a few flakes in alcohol, or the tincture may be pur- 
chased. 

Mercury. — For directions for keeping it clean and dry, see 
Botanical Gazette 22 : 471. Dec. 1896. 

Paraffin. — A common quality, melting at about 65 C. 

Phenolphtalein. — A few grams will last a long time. 

Potassic hydrate. — May be bought in sticks and the solution 
made, but it is more convenient to buy the liquor potasses of 
druggists. 

Sodium chloride. — Table salt is pure enough. 

Vaseline. 

APPARATUS FOR MORPHOLOGY. 

Dissecting microscopes. — Each pupil should be provided with one. 
A most effective low-priced dissecting microscope was designed 
by the author and is manufactured by several firms. In no case 
has the author any financial interest in the instruments. The 
stand T I, manufactured by the Bausch & Lomb Optical Co., 
Rochester, N. Y., with i-inch lens, and a similar one by Queen 
& Co., Philadelphia, have been approved by the designer. Many 
forms offered to schools by jobbers are not worth buying. 

Compound microscopes. — The school should be supplied with at 
least one good compound microscope for demonstrations, and as 
many more as can be profitably used. If the teacher is capable 
of using such instruments properly he will be able to select it 
wisely with such advice as he may obtain from personal acquaint- 
ances on whose judgment he can rely. Schools are advised to 
deal only with manufacturers of established reputation. 

Scalpels. — Each pupil should be provided with a sharp knife 
with slender blade for dissection. It is desirable for the school 
to furnish scalpels of suitable form. The slender blades, 3-3.5 
cm. long on cutting edge, are recommended. 

Forceps. — Straight form, with smooth points, will be found use- 
ful, though not indispensable. 

Needles. — Each pupil should have a pair of needles (No. 6, 



APPARATUS AND REAGENTS. 41 I 

sharps) with the eye end set into a soft pine penholder or similar 
handle. They must be kept sharp on a fine oil-stone. 

Drawing mad-rials. — A medium pencil (No. 3 or M) and a very 
hard one (No. 6 or 6 H) should be used and kept sharp. Slips of 
heaviest linen ledger paper (120 lb.) cut 14 X 8 cm. are recom- 
mended. Only one drawing should be put on a slip. 



APPARATUS FOR PHYSIOLOGY. 

Since much of the apparatus needs to be put together by the 
student, the requisites are mainly tools and a good supply of tub- 
ing, both glass and rubber, bottles, and bell jars. The following 
will enable the foregoing experiments to be carried out. 

Tools. — Hammer, fine saw, three or four chisels, assorted files, 
brace and assorted bits, screw-driver, smoothing plane, with a 
supply of nails (especially finishing nails) and screws will be 
found most useful. 

Glass tubing. — A little capillary tubing (0.5 mm. bore) will 
be needed. Most used sizes are 5 mm. (3 mm. bore), 7 mm. 
(5 mm. bore.) Some larger sizes (13 and 19 mm.) will also be 
useful. 

Rubber tubing. — 3 and 5 mm. bore mostly ; some of 10 and 15 
mm. bore. 

Bottles. — Wide-mouthed, various sizes, up to 1 liter. 

Tumblers. — Jelly glasses answer well. Odd lids and glass dishes 
from homes and stores can be made useful. 

Corks. — Assorted sizes. Several rubber stoppers, sizes S, 10, 12, 
3-hole, are desirable. 

Bell Jars. — Several sizes are necessary ; 1; X 20 and 20 X 30 cm. 
will be found useful; also at least one 30 X 50 1 in. All should 
have ground rim and tubulure at top. 

Funnels. — Glass, assorted sizes. <>, 8, and u cm. diam. are 
most used ; there should also be two or three larger ones. 

filter paper. — Buy cut filters 15 and iS cm. in diameter. 

Thermometers. — Should be graduated in degrees, — io° to -f- ioo° 
C, with milk-glass scale. 

Test tubes. — 2 X 15 cm. is a convenient size. 

T -tubes. — Two sizes. 5 and 10 mm. bore. 

Bunsen burners. — If gas is not available, gasolene burners 
should be substituted. 



412 APPENDIX. 

Marble-. — A plate 25 X 25 X 2.5 cm., polished on both sides. It 
can be re-polished after etching and used as often as desired. 

Filter pump. — Can be used if water service is available, or if a 
head of 5 m. can be secured by tank. Korting's is excellent. 

Rulers. — 30 cm. long, graduated in millimeters. 

Brushes. — Camelhair brush of large size, and sablehair, smallest, 
are useful. 

Pius. 

Tin tube. — 3 X 15 cm. See experiment 20. 

Absorbent cotton. — Also a roll of cotton batting. 

Sheet lead. — Light weight, used by plumbers. 

Plate glass. — Cut into pieces 20, 25, and 35 cm. square. 

Pine sawdust and clean sand. — For germinating seeds. 



APPENDIX IV. 
REFERENCE BOOKS. 

The following books will be found useful to teacher or pupil or 
both, and are recommended as suitable reference books for the 
school library. The list is not intended to be exhaustive, nor 
does it include books for popular reading. 

FOR GENERAL REFERENCE. 

Kerner: Natural history of plants. New York: Henry Holt & 
Co. $15.00. (Translated by Oliver.) 

Strasburger, Noll, Schenck and Schimper : Text-book of 
botany. New York : The Macmillan Co. $4.50. (Trans- 
lated by Porter.) 

Bennett and Murray : Handbook of cryptogamic botany. New 
York: Longmans, Green & Co. $5.00. 

Vines : A student's text-book of botany. New York : The Mac- 
millan Co. $3.75. 

Sachs : Lectures on the physiology of plants. New York : The 
Macmillan Co. $7.00. (Translated by Ward.) 

Goebel : Outlines of classification and special morphology. NY w 
York : The Macmillan Co. $5.50. (Translated by Garnsey 
and Balfour.) 

Warming: Handbook of systematic botany. New York: The 
Macmillan Co. $3.75. (Translated by Potter.) 

Gray : Systematic botany. New York : The American Book Co. 
$2.00. 

Bessey : Botany, Advanced Course. New York : Henry Holt & 
Co. $2.20. 

Geddes : Chapters in modern botany. New York: Charles 
Scribner's Sons. $1.25. 

413 



414 APPENDIX. 

Warming: Lehrbuch der iikologischen Pflanzengeographie. Ber- 
lin: Gebr. Borntrager. (A German translation by Knoblauch. 
An English translation is now in preparation.) 

PfeFFER : Pflanzenphysiologie. Ed. II., vol. I. Leipzig: Wil- 
helm Engelmann. M. 20. (An English translation is now in 
preparation by Dr. A. J. Ewart.) 

Vines : Lectures on the physiology of plants. New York : The 
Macmillan Co. $5.00. 

Goodale : Physiological botany. New York: The American 
Book Co. $2.00. 



FOR LABORATORY DIRECTIONS. 

Bergen: Elements of botany. Boston: Ginn & Co. $1.10. 

Spalding : Introduction to botany. Boston : D. C. Heath & Co. 
80 cts. 

Macbride : Lessons in elementary botany. Boston : Allyn & 
Bacon. 60 cts. 

MacDougal : Experimental plant physiology. New York : Henry 
Holt & Co. $1.00. 

Arthur : Laboratory exercises in vegetable physiology. Lafay- 
ette, Ind.: Kimmel & Herbert. (Pamphlet.) 35 cts. 

Darwin and Acton : Practical physiology. New York : The 
Macmillan Co. $1.60. 

Arthur. Barnes and Coulter : Plant dissection. New York : 
Henry Holt & Co. $1.20. 



APPENDIX V. 
OUTLINE OF CLASSIFICATION. 

In the foregoing work no endeavor has been made to present 
any scheme of classification, but only to develop certain principles 
in logical fashion. As a supplement the following general classi- 
fication, adapted mainly from Strasburger, Noll, Schenck and 
Schimper's Lehrbuch der Botanik, may be useful in showing the 
relationship of the more important plants named in the text and 
appendices. 

All classification is more or less artificial. The purpose of such 
an outline is to indicate roughly the present knowledge of kinship 
among plants. Even were knowledge perfect it would naturally 
be impossible to do this in a linear arrangement such as is neces- 
sary in a book. Moreover, knowledge is far from complete. It 
is to be expected, for example, that ultimately botanists will be 
able to express much more accurately the relationship between 
the groups of fungi and the algae than is now possible. Then, 
the various groups of fungi will be ranked alongside the green 
plants to which they are most akin, as is now done in the Schizo- 
phyta, instead of being constituted a class by themselves. 

The following classification differs more or less from all others 
in details. Like them, it is merely tentative, and will be modified 
as knowledge increases. Only in the most general divisions will 
all schemes be found similar. 

Subkingdom I. THALLOPHYTA. Thallophytes. 

Class I. Myxomycetes. Slime molds. 
Class II. Schizophyta. Fission plants. 

Order I. Schizophycece. Fission alga?. Blue-green algae. 

Nostoc. Rivularia. Oscillaria. 
Order 2. Schitomycetes. Fission fungi. 
Bacteria. 

415 



416 



APPENDIX. 



Class III. Diatomeae. Diatoms. 

Class IV. Peridineae. Often ranked as animals. 

Class V. Conjugate. Brook silks and desmids. 

Spirogyra. Zygnema. Mesocarpus. Desmids. 
Class VI. Chlorophyceae. Green algae. 
Order I. Protococcales. 

Pleurococcus. Volvox. 
Order 2. Cottfervoidales. Confervoid algae. 
Ulothrix. Cladophora. Ulva. 
Order 3. Siphonales. 

Vaucheria. Caulerpa. Acetabularia. 
Class VII. Phaeophyceae. Brown algae. 
Order 1. Phaosforales. 1 

Lessonia. 
Order 2. Fucales. 1 

Fucus. Sargassum. 
Order 3. Dictyotales. 
Class VIII. Rhodophyceae. Red algae. 

Orders numerous. Polysiphonia. 
Class IX. Characeae. Stoneworts. 
Chara. Nitella. 
Class X. Hyphomycetes. True fungi. 

A. Phycomycetes. Algoid fungi. 



Heterogamous Series. 
Sub-class I. Oomycetes. 
Orders numerous. Cys- 
topus. 



B. Mesomycetes. 
Sporangiate Series 
Sub-class III. Hemiasci. 
Yeast. 

C. Mycomycetes 
Sporangiate Series. 
Sub-class V. Ascomycetes. 
Witch-broom fungus. Mil- 
dews. Truffles. Penicil- 
lium. Cup-fungi. Morels. 
Class XI. Lichenes. Lichens. 

Physcia. Theloschistes 
1 Various larger species known as tangles, kelp, r 



Isogamous Series. 
Sub-class II. Zygomycetes. 
Orders numerous. 

Mucor. Rhizopus. Em- 
pusa. 
Intermediate fungi. 

Non-sporangiate Series. 
Sub-class IV. Hettribasidii. 
Brand fungi. Smuts. 
Higher fungi. 

Non-sporangiate Series. 
Sub-class VI. Basidiomy- 

cetes. 
Rusts. Cap-fungi. Poly- 
porei. Puff-balls. 



.k-weed, bladder-wratk. 



OUTLINE OF CLASSIFICATION. 417 



Subkingdom II. BRYOPHYTA. Bryophytes. Mossworts. 

Class I. Hepaticae. Liverworts. 
Order 1. Ric dales. 

Riccia. 
Order 2. Marchantiales. Liverworts. 

Marchantia. Lunularia. 
Order 3. Anthocerotales. Horned liverworts. 
Order 4. Jungermanniales. Leafy liverworts. Scale mosses. 

Porella. 
Class II. Husci. Mosses. 

Order 1. Sphagna Us. Peat mosses. 

Sphagnum. 
Order 2. Andreaales. 
Order 3. Archidiales. 
Order 4. Bryales. True mosses. 

Bryum. Mnium. Hypnum. 



Subkingdom III. PTERIDOPHYTA. Pteridophytes. 
Fernworts. 

Class I. Filicineae. 

Order 1. Filicales. True ferns. 

Adiantum. Pteris. Aspidium. Asplenium. 
Order 2. Hydropteridales. Water ferns. 
Class II. Equisetineae. Horsetails. Scouring rushes. 

Equisetum. 
Class III. Lycopodineae. 

Order 1. Lycopodiales. Ground pines. 

Lycopodium. 

Order 2. Selaginellales. Club mosses. 

Selaginella. 



Subkingdom IV. SPERMATOPHYTA. Seed plants. 



Class I. Gymnospermae. Gymnosperms. 
Order 1. Cycadales. Cycads. 
Cycas. 



41 8 APPENDIX. 

Order 2. Coniferales. 

Pines, spruces, larches, firs, etc. 
Order 3. Gnetales. 

Welwitschia. 
Class II. Angiospermae. Angiosperms. 

Sub-class I. Monocotyledon.es. Monocotyledons. 

Orders several. Lilies, irises, grasses, sedges, rushes, 
palms. 
Sub-class II. Dicotyledones. Dicotyledons. 

Orders numerous. Most herbs with net-veined leaves, 
deciduous shrubs and trees. 



INDEX. 

All references are to pages. When there are two or more references to the 
same topic, figures in bold-face indicate the definition or chief discussion of the 
subject. Italic figures indicate illustrations. 



Absorption, carbon dioxide 165 ; 
water 74, 153, 155, 323 

Acacia, leaves I : ' t 

Acetabularia 23, l'4 

Achillea, inflorescence 257 

Achlya, sex organs 293 

Acids, carbon 175 

Adaptations 146, 308 

Adiantum 382; embryo 62, 68; 
leaf 126; spermary 282 

Aeration 171 

Agaricus 377, 404 

Agrimonia, fruit 866 

Ailanthus, fruit 864 

Air, distributing seeds 363; dis- 
tributing spores 356; effect of 
composition 312 ; effect of 
moisture in 316; -plants 152 

Alcanna, corolla 250 

Aldrovandia ..'}>: 

Aleurone grains 169 

Algae, eggs ?86, 288; fission 8; 
gametes 278; imprisoned 338, 
877 ; in other water plants 33 1 

Alkaloids 177 

Allium, stem 106 

Aloe, epidermis 828 

Alternation of generations 49. 
60 

Amanita, fructification 219 

Amorpha, sleep movement .'". v 

Amorphophallus, leaf 125 

Anabaena 10 

Anabolism 166 

Anagallis, fruit SOS; pistil :','> 

Anaptychia, apothecium 



Angiosperms 237; ovary 291; 

seed 299; sperr.iary 281 
Animals, and plants 336, 338, 

342; distributing seeds 365; 

distributing spores 357 
Anther 246 

Anthyllis, venation 137 
Ants and plants 348 
Apical cell, Cha.ra.SO, 31; Funis 

34', liverworts 51; Polysipho- 

nia 32; root 67, 6S; shoot 84 
Apodanthes S40 
Apogamy 294 
Apparatus 409 
Apple, fruit S05 
Arbor vitae, shoot 97 
Archegonium 289 
Arisarum, flower 
Armor, protective 347 
Artemisia, hail 
Ash, pistil of .;/ 
Asparagus, branches 92 
Aspidium, pinnule 280; s.irus 

281; sporangium 
Asplenium, buds 262; gamete* 

phyte 60 
Assimilation 1 62 

Astragalus, pistil 
A ulai omnium, brood bud 
Automatism u^. 188 
Auxanometer isn 

Bai tei ia to, //. 12 
Bacterium aceti // 
Balsam, stem 6 
I tai berry, thori 

,19 



420 



INDEX. 



Bark 111, 116 

Bast, secondary 113 

Bazzania 53 

Bean, geotropic roots 199, 201 

Beech, mycorhiza 336 

Beet, stoma 184 

Begonia, stem bundle 104 

Bellflower, fruit 802; leaf ro- 
sette 196 

Bidens, fruit 367 

Bird's-nest fungus 218 

Blackberry 305 

Bladderwort 343. 344, 345 

Blade, leaf 123; structure of 
leaf 133 

Blasia 54 

Boletus 404 

Books, reference 413 

Bracts 131, 236, 256 

Branches, dwarf 90, 91, 92 

Branching 22; of leaves 122, 
124, 125, 126, 128, 138; of liv- 
erworts 51; of mosses 57; re- 
production by 267; of root 78; 
of shoot 86; of stamens 249 

Brood buds 260 

Bryony, tendril 94 

Br yum, capsule 58, 228, 280; 
section of stem 56 

Buckthorn, leaf 128 

Buds, 85, 88; adventitious 89; 
axillary 87; dormant 89; on 
roots 81; reproductive 263; 
shoot 85 

Budding 40, 211, 267 

Bulb 90, 326 

Bulblets 93 

Bundles, vascular 71, 72, 100, 
103, 114, 132, 136 

Butomus, anther 248 

Butternut, buds 88 

Cactus, forms 98 

Calamus, root 72 

Caltha 389. 407 

Calyptospora, haustoria ^5; 
spores 854 

Calyx 237, 253 

Campanula, fruit 302; leaf ro- 
sette 196 

Canna, leucoplasts 4 



Capsella, embyro 66; pistil 242 

Carbohydrates 159; manufac- 
ture 166 

Carbon dioxide, absorption 165 

Carex, leaf edge 348 

Carnivorous plants 342 

Carpels 235, 236, 237 

Carpogonium 287 

Carrot, chromoplasts 6 

Caulerpa 23, 24, 25 

Cecropia, stem 349 

Cedar, gametophytes 284 

Cell 1; division 17, 18; naked 
147; wall 5 

Centrifuge 199 

Centrospheres 4 

Cereus, shoot 98 

Chara27, 2S, 30,2,11, 402; ovary 
281; spermary 2S0, 881 

Characeae 27 

Cheiranthus, hairs 101 

Chelidonium, hair cell 191 

Chemotaxis 274 

Cherry, cork cambium 110; 
fruit 304 

Chlorophyll, function 166; spec- 
trum 166, 16? 

Chloroplasts 4, 5, 21; move- 
ments 192 

Chondromyces, colonies 884 

Chromoplasts 5 

Cilia 12, 147, 190 

Cinchona, bark 112; stem 108 

Cinnamon, flower 248 

Cladonia 377 

Cladophora 22, 28, .'./, 370, 402 

Cladophylls 92 

Classification 415 

Clavaria, fructification 219, 404 

Claviceps, fructification /.'. ' 

Climate, relation of plants to 
308 

Climbers 330 

Close-pollination, adaptations 
for 358 

Clover, root tubercles 337 

Club-mosses, sporangia 231 

Clusia, periderm of root 74 

Cobsea, flower 360 

Cockle-bur, fruit 367 

Ccenocytes 22 



JXDEX. 



421 



Cohesion, carpels 241; stamens 
248 

Cold, protection against 315 

Colonies, gelatinous 8 

Color, significance 359 

Conducting tissues 156 

Cone, pine 998 

Conifers, fruit 29S 

Conjugatae 16, 20 

Conjugation 269, 274 

Contact movements 203 

Contractility 145 

Convolvulus, hairs 321 

Coprinus, gill 217 

Cosmos, stamens 249 

Cotton, fruit 366 

Cotyledons 117 

Cork 110; cambium no 

Corm 90 

Corn, stem bundles 107 

Cornus, inflorescence 257 

Corolla 237, 253 

Coronilla. sleep movement 207 

Cortex, Chara 30; leaves 135; 
root 72, 73; secondary 109; 
stem 100, 109 

Cranberry rust, spore chain 354 

Crataegus, stipules 121 

Cross-pollination 255; adapta- 
tions for 358 

Crucibulum 21S 

Crystals 175, 176, 351 

Cup fungus 223 

Currant, nectary 177; ovules 

Cuscuta 889 

Cutin 6 

Cuttings 266 

Cycas, carpel 238; seed 897 

Cystocarps, Polysipbonia 988, 

£89 
Cystopus 277, 375, 403 
Cytoplasm 2 

Dandelion, fruit 866 

Datura, anther 248; leaf mo- 
saic 196 

Dehiscence, anthers 247; fruit 
301, 80S, 808 

Development, phases of 178 

Desmids 16 



Desmodium fruit 366 

Diatoms 14, 16 

Dichotomy 78, 86 

Digestion 162; intracellular 170 

Dionaea 346; leaf 208, 34-5 

Distribution, of seeds 361; of 

spores 353 
Dodder 889 

Dogwood, inflorescence 257 
Domatia 350 
Dorsiventrality 57 
Draba, hairs 822 
Dracaena, stem 114 
Drosera, leaves 345 
Duration, of root 73; of shoot 

94 

Echinocactus, shoot 98 

Ecology 144, 307 

Edelweiss, hairs 321 

Eel grass, runners 265 

Egg 285 

Elaeagnus, scales 322 

Elaters 7, 355 

Elatine, stem 102 

Elder, lenticel US 

Elm, buds 88; cork cambium 

110 
Emergences 101, 102, 802 
Embryo 62, 63, 66,289,291, 295, 

296, 297, 300, 304; sac 243, 

244 
Empusa 354 
Endodermis, root 72, 75, 77; 

stem 100, 115 
Endosperm 298, 299 
Energv, released by respiration 

173 ' 
Entoderma in alga 
Enzymes 162 
Epidermis, adaptations 320; of 

leaf 133; of root 70; of stem 

100, 101 
Epipactis, cell division 17 
Epiphytes 331 
Epispore 214 
Equisetum 230, 282, 384; apical 

bud 8J t ; sporangium wall 988) 

spore- 
Ergot, fructification .;?. 
Erysiphe 924, 375; f™' 1 



422 



INDEX. 



Eschscholtzia, ovules 243; pro- 
tection of stamens 353 
Excretion 173 
Exobasidium 43 

Fagus, mycorhiza &?<? 

Fats 160 

Fennel, resin receptacle 176 

Fermentation 162 

Fern, maidenhair 3S2, 406 

Fernworts 60; ovary 290; sper- 
mary 280, 282; sporangium 
229, 356 

Fertilization 255, 285 

Fig, inflorescence 260 

Filament 246 

Fir, seed 297; seedling 118 

Fission 17, 211 

Flax, stem 104 

Flower 92, 236; leaves 131; 
movements 196 

Fly fungus 354 

Fly trap, leaves 208, 345 

Foliage 119 

Food, for insects 359; insects as 
342; with spores 215 

Foods 159; manufacture 166, 
16S; storage 16S; transloca- 
tion 168 

Fossombronia 54 

Fragmentation 211 

Fraxinus, pistil 241 

Freezing, protection against 
315 

Fructifications 218 

Fruits, accessory 304; adapta- 
tions to distribution of seed 
361; of angiosperms 300; dry 
300; fleshy 303, 3(17; of gym- 
nosperms 298; multiple 305 

Fucus 33, 34, 373, 4°3; egg 286; 
ovary 287, 288; spermary 278 

Funaria, leaf 56; development 
of sporophyte 206; ovary 290 

Function 143; limits to 146; unit 
of 144 

Fungi 39, 213, 216 ff., 335, 337, 
338; fission 10; loss of sex- 
uality 293 

Fusion, of hyphae 45; of sta- 
mens 249 



Gametophyte 49; of fernworts 
60; of liverworts 58, 54; of 

mosses 55; reduction 61, 292; 
of seed plants 64; shoot 82 

Gaultheria, fruit S04 

Gelatin 6, 12 

Gemmae 260 

Geotropism 197 

Gerardia, parasitic SS9 

Germination, adaptations to 
367; of pollen 251 

Glceocapsa S 

Grafting 267 

Grain 301 

Grasses, geotropic node 199, 
200; lea.H20; rolling of leaves 
S19 

Grimmia, capsules 855 

Growth 151, 178; conditions of 
183; daily period 1S5; dura- 
tion 187; grand period 1S1 ; 
induced 295; intercalary 38; 
of leaves 137, 138; localiza- 
tion of 22; measuring 180; 
movements due to 192; of cell 
wall 7; of spores 215; region 
of 181; spontaneous varia- 
tions in 1S7 

Gymnosperms 237; ovary 291; 
seed 297; spermary 280, 282 

Hairs 320, 821, 822, 347; absorb- 
ing 323; glandular 360; of 
stem 101 

Halophytes 311, 326 

I laustoria 45, 46 

Heat from respiration 174 

Heatli, rolled leaf 821 

Heliotropism 194 

Hellebore, pistil .' :} 1 

Helotism 333, 337 

Heterocysts 9 

Heterogamy 271, 276 
Hibernacula 204 
Honeysuckle, buds SS; leaves 

128 
Hop, emergences 202 
Horse-chestnut, leaf 126 
Horsetails 384, 405; sporangia 

230, 232; sporangium wall 

§88; spores ..;.; 






INDEX. 



423 



Host 161 

Houseleek S25 

Hydnum, fructification 220, 404 

1 [ydrophytes 311, 327 

Hydrotropism 202; apparatus 
SOS 

II ylocomium 56 

Hyphse 39; branching 40; fu- 
sion 45 

Indian turnip, inflorescence 256 
Infection with fungi 43 
Inflorescence S7 
Insects, adaptations of flowers 

to 358; distributing spores 

357; exclusion of 359; as food 

342 
Integuments, of ovule 243; of 

seed 299 
Internodes 96; of Chara 27 
Involucre 256 

Irregularity 254; purpose 359 
Irritability 145, 183, 188, 274; 

localization 189 
Isogamy 271, 274 
Ivy, chloroplasts 4 

Katabolism 170, 175 

Land plants 152, 311 

Larch, gametophyte 282, 283; 
shoot 320 

Lasiagrostis, rolling of leaf S19 

Lathyrus 407 

Leaves, adaptation 314, 320; 
arrangement 119; base 120; 
blade 123; development 117; 
fall of 140; form 119; growth 
137. 138; of mosses 57; origin 
53; pine 91, 92; primary 117; 
secondary 117; stalk 122; 
structure 132, 189; suppres- 
sion 319; as water recepta- 
cles 324 

Leguminosfe, root tubercles 336 

Lenticels 113 

Leucoplasts .'/, 5 

Lichens J'., 47, .'.'.7, 337 

Light, effect on growth [84, 
185; effect on form 313; effect 
on water plants 33S; escaping 



319; produced by plants 17c 

relation to photosyntax 166 
Lignification 6 
Lily, anther .'/,S; buds 262 
Lime, effect of 317 
Linden, domatia 350; shoot 86 
Liverwort 49, 378, 379, 404, 405; 

sporangium 227 
Locomotion 190 
Locust, development of leaf 

139; stipule thorns ISO 
Lodgers 334 
Lonicera, buds S8 
Lotus, fruit SOS 
Lunularia %9, 50 
Lychnis, petal 254; stigma 2j0 
Lycopodium, stem 103 

Malt 40S 

Maple, buds 88; fruits S24; leaf 
188; mosaic 195 

Marchantia 378, 404; elaters 7 
rhizoids 7; spermarv 979 
thallus 267; brood-buds 262 
thallus 261 

Marigold, marsh 389, 407 

Marsilia, root tip 68 

Mechanical tissues 149; devel- 
opment of 1S6 

Mechanics of body 149 

Megasporangium 234 

Megaspore 231; of lily .' 

Melampsora, spore beds 215 

Meristem, primary 35; of root 
68; of shoot 84; secondary 74, 
108 

M>s, 1, arpus 21; conjugating 

Mesophytes 311, 312 
Metabolism 145, 215 
Metzgeria ■'•-' 
Micrococcus // 
Microsphaera 375, 403 
Microsporangium 234 
M i< rospores 231 

Mildew :."/. 375, 403; fru • 

Milkweed, Bowers 252; pollen 

mass 
Mimicry 3 p 

Mimosa, leaves 208; sleep 
movement ."- , 



424 



INDEX. 



Mineralization 7 

Mnium 381, 405 

Moisture, effect on growth 186 

Monopodial branching, of root 
7S; of shoot 87 

Monostroma 26 

Monotropa, pollen tube 283 

Morchella, fructification 286 

Morning glory, chloroplasts 4; 
seedling US 

Mosaic, leaf 195, 106 

Mosses 53, 3S1; brood buds.?'/'.'; 
sporangium 229; teeth 355; 
sporophyte 822 

Mossworts, ovary 289; sper- 
mary 2S0 

Motor organs 192, 295 

Mountain ash, chromoplasts 6 

Mousetail, flower 259 

Movements 188; combined 196; 
contact 203, 207; for entrap- 
ping animals 345; of water, 
effect on plants 328; para- 
tonic 193; photeolic 206; spon- 
taneous 193, 206; to protect 
spores 352 

Mucor 41, 403; sporangium 222 

Mulberry 306; flower and fruit 
305 

Mushroom 377, 404; gill SI? 

Mustard seedlings, geotropic/.%? 

Mutualism 333 

Mycelium 41 

Mycorhiza 335, 336 

Myosurus, flower 259 

Nectar 176; guides to 359 

Nectaries 177 

Nemalion, ovary 288 

Nettle hair 348 

Nitella 27, ."■> 

Nitrogen, supply 342 

Nodes 96; of Chara 27 

Nostoc 9, 369, 401 

Noteroclada 54 

Nucleus 3 

Nutation 193 

Nutrition 151; of Oscillaria 10 

Oats, cell from leaf 4; epider- 
mis 134 



Odor, cause 176; purpose 359 

Offsets 90, 265 

Oils 176 

Oleander, leaf 824 

Oleaster, scales 822 

Oligotrichum, leaf 56 

Onion, embryo 56; stem 106 

Oogonium 287 

Opuntia 321 

Orange, oil receptacle 177 

Orchid, chromoplast 6; light 
seeds 363; mycorhiza 886 ; 
pollen tube 283 

Organ 143 

Origin of roots 79 

Orthotrichum, branching 57 

Oscillaria 10, 370, 401 

Osmosis 156 

Ovary 240, 273, 286 

( Hulury 240 

Ovules 237, 242, 243, 244; dia- 
grams 285 

Oxalis, cells 102 

Oxygen, effect on growth 186; 
supply 171 

Pansy, seed 300 

Parasites 43, 161, 163 

Parasitism 333, 338 

Parmelia, thallus 825 

Pea, flower 255; growth of root 
182 ; leaf tendrils 130 ; root 
branches 79; sweet 407 

Pellia, sperms 280 

Peperomia, water storing 326 

Pepper, fruit 800 

Perennials in 

Perianth 236, 252 

Pericarp 300; adaptations to 
distribution of seeds 3(12 

Pericycle, root 71 ; stem 100, 
103' 

Periderm, root 74, 75; second- 
ary in; stem 109 

Perisperm 29S, 299 

Peronospora, haustoria 46; sex 
organs 87? 

Petal 237 

Petiole 122; scarlet runner 105', 
sensitive 128; structure 132 

Peziza 223, 376, 404 



INDEX. 



425 



Phascum, sporophyte 59 
Phaseolus, motor organs 905; 

stele of root 75, 76 
Phelloderm 109 
Phloem, bundle of root 72 ; 

secondary 109 
Photosyntax 166; product 167; 

and respiration 171, 175 
Phycocyanin 8 
Phycoerythrin 33 
Phycophaein 3S 
Phyllodia I:', 
Phyllotaxy 119 
Physcia 376, 404 
Physiology 143; apparatus 411; 

experiments 391 
Phytolacca seed 300 
Pilobolus, abjection of sporan- 
gium S5S 
Pilularia, megaspore 214 
Pimpernel, fruit SOS; pistil £45 
Pine 387, 406; carpel 238; cone 

298 ; shoot 91 ; wood, pene- 
trated by hyphae 44 
Pineapple 306 
Pine sap 988 
Pistil 237; diagram £85; simple 

and compound 240 
Pitcher plants 129, 342, S48 
Pitfalls 342 

Pith, rays 115; stem 107 
Placenta 244 
Plasmodia 14S 
Plastids 4 

Plectranthus, hairs 101 
Pleurococcus 13, 369, 401 
Pokeberry, seed SOO 
Pollen, grains 249, 250 ; tube 

."/", 281, ?8S, ?84, 886 
Pollination 255, 358 
Polyembryony 294 
Polygonatum, leaf VB7 
Polygonum, megaspore 

Stipules /.'./; tubers U) 
Poly podium 61 
Polyporus 4.! ; fructification 

i£0, 404 
Polysiphonia 31, St, 372, 402; 

cystocarps $88, £89 ; tetra- 

s pores .'.',' 
Folytrichum 55 



Pondweed, hibernacula 268 

Poplar, mycorhiza 335 

Poppy, ovules 243; protection 

of stamens 353 
Porella 379, 405 
Potassium salts, relation to 

photosyntax 167 
Potato, pistil 241 ; starch 5 ; 

seedling ?66 
Pressure, effect on growth 186; 

root 156 
Prickles 101, K/J, 347 
Proteids 160; grains 169; manu- 
facture 168 
Prothallium 60 
Protonema, mosses 58 
Protoplasm 2; movements 191; 

naked 147; powers 145 
Psychotria, domatia 350 
Pteris, embryo 62 ; origin of 

root SO; ovary 290 
Puff ball 214, 221 
Putrefaction 162 
Pyrenoids 21 
Pyrola, fruit 302 

Radiolarian and algae 33S 

Rainfall, adaptations to 316 

Ranunculus, leaf 120; nectary 
177 

Raspberry 305 

Reaction 189 

Reagents 409 

Rejuvenescence 268 

Repair 151 

Reproduction 145, 209; adapta- 
tions 352; sexual 268; vegeta- 
tive 211 

Resins 176 

Respiration 171; intramolecular 
172 

Rheum, flower .">■'' 

Rhizoids 22; Chara 31; liver- 
worts 50; mosses 53 

Rhizome 90 

Rhizopus 374, 403 

Rhododendron, anthers and 
pollen . '/.'' 

Riccia 50 

Rigidity, how secured 149 

Rings, annual, of stem 116 



426 



INDEX. 



Rivularia 369, 401 

Robinia, thorns ISO 

Root 65; adaptations 156; ad- 
ventitious 267 ; aerial 324 ; 
cage 200, 201; cap 68, 70, 71; 
climbers 331 ; differences 
from shoot 85 ; fleshy 77 ; 
float 77; hairs 69, 70; hairs 
and soil 154; hairs, solvent 
action 155; origin from leaves 
139 ; parasitic 889 ; pressure 
156; pressure, apparatus for 
157; primary 65; secondary 
67 ; tap 324 ; tendrils 78 ; 
thorns 7S ; tubercles 336 ; 
woody 76 

Rose, flower 260; leaves 122 ; 
prickle 102; seedling IIS 

Rotation of protoplasm 191 

Runner 90, 265 

Rye, daily period of growth 
185; stem IS 4 

Sage, anther 247 
Salts in water 154, 164 
Salvinia, sporangium 285 
Saprolegnia, zoospores 213 
Saprophytes 161 
Sarcina 11 
Sargassum 37, 38 
Saxifrage, flower 360 
Scales 320, 322; leaf 130 
Scarlet runner, motor organs 

205 
Scions 266 

Scutellaria, cortex 109 
Secretion receptacles 176, 177 
Sedge, leaf edge 848 
Sedum, flower .'/..', 259; offsets 

.<•■; 

Seed 296, 407; in angiosperms 

299; distribution 306, 361; in 
gymnosperms 297 

Seed plants, ovary 290 ; para- 
sitic 340 ; spermary 280 ; 
spores and sporangia 234 

Selaginella 386, 406 ; female 
gametophyte 291 ; male ga- 
metophyte 282; stem 105 

Selection, power of 164 

Sempervivum 826 



Sepal 238, 253 

Sex organs 273 

Sexuality, imperfect 269; loss 
of 293; origin 268 

Shepherd's purse, embryo 66; 
pistil 242 

Shoot 82; differences from root 
S5; from leaves 139; liver- 
worts 52; primary 83 

Sleep movements 206 

Soil 153; effect of temperature 
of 315 ; effect of physical 
characters 317; limits of ab- 
sorption from 155 ; salts in 
154; water in 154 

Solutions, water 152 

Spadix 256 

Spathe 256 

Spermary 274, 277 

Sperms 276 

Sphseroplea, gametes, 286 

Sphagnum, sporophyte 228 

Spirogyra 20, 370, 401 ; conju- 
gating 272 

Splachnum, capsules 58 

Sporangia 216, 221; of anther 
247; of fern 356 

Spore 212; chains 217; diagram 
216; germinating 4- : '< non- 
sexual 212; of Penicillium 211 ; 
of Filularia 214; protection 
352; resting 294; sexual 268 

Sporophylls 131, 230 

Sporophyte 49, 227, 292; fern- 
worts 62; mosses 58, 59, :::; 
shoot 83; seed plants 64 

Spruce, ovaries 284 

Stamens 235, 236, 245 

Starch, manufacture 167 ; re- 
serve 169 

Stem 96; climbing 99; erect 98 
forms of xerophytic 319; o 
mosses 55, 56; prostrate 98 
sections 99, 102, 108, 104, 105 
106, 108, 114; shape 97; struc 
ture 99; twining 99 

Stele, of leaves 136; of root 71; 
of stem 100, 103 

Stigma 240 

Stimulus 188; transmission of 
190 



INDEX. 



427 



Stipules 121 

St. John's wort, stamens 250, 
251 

Stolon 90 

Stomata 134; sunken 322 

Stonecrop, flower 259; offsets 
264 

Storage 107; of foods 168, 169; 
in leaves 131; in roots 77 

Strawberry, flower 258, 259; 
runners 264 

Streaming of protoplasm 191 

Style 240 

Suberin 6 

Sugar, manufacture 167 ; re- 
serve 169 

Sugar cane, epidermis 323 

Sundew, leaves 345 

Suspensor 66, 291 

Symbionts 161 

Symbiosis 161, 333 

Symphoricarpus, fruit cells 179 

Sympodial branching, in moss 
57; in shoot of seed plants 86 

Syrrhopodon, brood buds 262 

Telegraph plant, leaf 206 
Temperature, effect on growth 

185; on form 314; on water 

plants 328 
Tendril, of bryony 94; leaf 130; 

movement of 203; shoot 93 
Tension, distributing seeds 

362; distributing spores 355; 

of tissues 149, 182 
Tetragonolobus, sleep move- 
ments 207 
Tetrasporangia, of Polysi- 

phonia .'.',' 
Thallus 22, 25; of Fucus 34; of 

liverworts 49 
Thickening, secondary, of root 

74, 77; of stem 107, 115 
Thlaspi, leaf VSS 
Thorn apple, anther 248 
Thorns 347; leaf 130; shoot 93; 

of Veil a 96 
Thyme, anther 247 
Tococa, base of leaf 350 
Torus 236, 258 
Traction, effect on growth 186 



Trametes 44 
Transfer of foods 168 
Transpiration 158; adaptations 

for reducing 318 
Traps 343 

Trefoil, fruit of tick $66 
Tropaeolum, leaf 128 
Tubers 93, 326 
Turgor 148; distributing seeds 

362; distributing spores 353; 

movements 204 
Twiners 201, 331 
Tylanthus, leaf 321 

Ulothrix 21; reproduction 270, 

271; zoospores 269 
Ulva 26 
Uncinula 403 
Urtica, hair 348 
Utricularia 343, 344, 345 
Uvularia, leaves 128 

Vacuoles 2, 179 

Vallisneria, distribution of 

spores 356, 857; runners 265 
Vanda, light seeds 868 
Vanilla, leucoplasts 5 
Varnish, on epidermis 321 
Vascular bundles 71, 72, 100, 

103, 114, 132, 136 
Vaucheria 22, 23 ; sex organs 

278 
Vella, thorns 95 
Venation, leaves 125, 127, 137, 

13S 
Veratrum, pistil .'.;/ 
Vicia, vascular bundles of root 

75 
Violet, anther 2 40; fruit /.v.' 

Water, absorption 153, 323 ; 
distributing seeds 362; dis- 
tributing spores 356 ; effect 
of composition 329; effect of 
movements 32S; force raising 
157; loss 158; movement 150; 
necessity 152 ; path of 156 ; 
percentage 151 ; -plants 152, 
327; salts in K14; storing 325 

Waste products 175 

Wax, on epidermis 321 



428 



INDEX. 



Weight, loss of 173 
Welwitschia 140 
Willow, fruit S65; leaf 127 
Wind, distributing seeds 363; 

distributing spores 356; effect 

on form 313 
Wings to fruits 364 
Wintergreen, fruit 302, 304 
Wheat, flower 258; geotropic 

stem 200; seedling 11S 
Wood, in root 71; secondary 113 

Xanthium, fruit 367 



Xerophytes 311, 318 
Xylern bundles, of root 72; sec 
ondary 109 

Yarrow, inflorescence 257 

Yeast, beer 40 

Yew ovule and fruit 239 

Zamia, flower 233 
Zea. stem bundles 107 
Zoospores i^T, 212 
Zygnema 20, 401 



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